=encoding utf-8

=head1 NAME

Net::SSLeay - Perl extension for using OpenSSL

=head1 SYNOPSIS

  use Net::SSLeay qw(get_https post_https sslcat make_headers make_form);

  ($page) = get_https('www.bacus.pt', 443, '/');                 # Case 1

  ($page, $response, %reply_headers)
	 = get_https('www.bacus.pt', 443, '/',                   # Case 2
	 	make_headers(User-Agent => 'Cryptozilla/5.0b1',
			     Referer    => 'https://www.bacus.pt'
		));

  ($page, $result, %headers) =                                   # Case 2b
         = get_https('www.bacus.pt', 443, '/protected.html',
	      make_headers(Authorization =>
			   'Basic ' . MIME::Base64::encode("$user:$pass",''))
	      );

  ($page, $response, %reply_headers)
	 = post_https('www.bacus.pt', 443, '/foo.cgi', '',       # Case 3
		make_form(OK   => '1',
			  name => 'Sampo'
		));

  $reply = sslcat($host, $port, $request);                       # Case 4

  ($reply, $err, $server_cert) = sslcat($host, $port, $request); # Case 5

  $Net::SSLeay::trace = 2;  # 0=no debugging, 1=ciphers, 2=trace, 3=dump data

  Net::SSLeay::initialize(); # Initialize ssl library once

=head1 DESCRIPTION

L<Net::SSLeay> module contains perl bindings to openssl (L<http://www.openssl.org|http://www.openssl.org>) library.

B<COMPATIBILITY NOTE:> L<Net::SSLeay> cannot be built with pre-0.9.3 openssl. It is strongly recommended
to use at least 0.9.7 (as older versions are not tested during development). Some low level API functions
may be available with certain openssl versions.

It is compatible with OpenSSL 1.0 and 1.1. Some functions are not available under OpenSSL 1.1.

L<Net::SSLeay> module basically comprise of:

=over

=item * High level functions for accessing web servers (by using HTTP/HTTPS)

=item * Low level API (mostly mapped 1:1 to openssl's C functions)

=item * Convenience functions (related to low level API but with more perl friendly interface)

=back

There is also a related module called L<Net::SSLeay::Handle> included in this
distribution that you might want to use instead. It has its own pod
documentation.

=head2 High level functions for accessing web servers

This module offers some high level convenience functions for accessing
web pages on SSL servers (for symmetry, the same API is offered for
accessing http servers, too), an C<sslcat()> function for writing your own
clients, and finally access to the SSL api of the SSLeay/OpenSSL package
so you can write servers or clients for more complicated applications.

For high level functions it is most convenient to import them into your
main namespace as indicated in the synopsis.

=head3 Basic set of functions

=over

=item * get_https

=item * post_https

=item * put_https

=item * head_https

=item * do_https

=item * sslcat

=item * https_cat

=item * make_form

=item * make_headers

=back

B<Case 1 (in SYNOPSIS)> demonstrates the typical invocation of get_https() to fetch an HTML
page from secure server. The first argument provides the hostname or IP
in dotted decimal notation of the remote server to contact. The second
argument is the TCP port at the remote end (your own port is picked
arbitrarily from high numbered ports as usual for TCP). The third
argument is the URL of the page without the host name part. If in
doubt consult the HTTP specifications at L<http://www.w3c.org>.

B<Case 2 (in SYNOPSIS)> demonstrates full fledged use of C<get_https()>. As can be seen,
C<get_https()> parses the response and response headers and returns them as
a list, which can be captured in a hash for later reference. Also a
fourth argument to C<get_https()> is used to insert some additional headers
in the request. C<make_headers()> is a function that will convert a list or
hash to such headers. By default C<get_https()> supplies C<Host> (to make
virtual hosting easy) and C<Accept> (reportedly needed by IIS) headers.

B<Case 2b (in SYNOPSIS)> demonstrates how to get a password protected page. Refer to
the HTTP protocol specifications for further details (e.g. RFC-2617).

B<Case 3 (in SYNOPSIS)> invokes C<post_https()> to submit a HTML/CGI form to a secure
server. The first four arguments are equal to C<get_https()> (note that
the empty string (C<''>) is passed as header argument).
The fifth argument is the
contents of the form formatted according to CGI specification. 
Do not post UTF-8 data as content: use utf8::downgrade first. In this
case the helper function C<make_https()> is used to do the formatting,
but you could pass any string. C<post_https()> automatically adds
C<Content-Type> and C<Content-Length> headers to the request.

B<Case 4 (in SYNOPSIS)> shows the fundamental C<sslcat()> function (inspired in spirit by
the C<netcat> utility :-). It's your swiss army knife that allows you to
easily contact servers, send some data, and then get the response. You
are responsible for formatting the data and parsing the response -
C<sslcat()> is just a transport.

B<Case 5 (in SYNOPSIS)> is a full invocation of C<sslcat()> which allows the return of errors
as well as the server (peer) certificate.

The C<$trace> global variable can be used to control the verbosity of the
high level functions. Level 0 guarantees silence, level 1 (the default)
only emits error messages.

=head3 Alternate versions of high-level API

=over

=item * get_https3

=item * post_https3

=item * put_https3

=item * get_https4

=item * post_https4

=item * put_https4

=back

The above mentioned functions actually return the response headers as
a list, which only gets converted to hash upon assignment (this
assignment looses information if the same header occurs twice, as may
be the case with cookies). There are also other variants of the
functions that return unprocessed headers and that return a reference
to a hash.

  ($page, $response, @headers) = get_https('www.bacus.pt', 443, '/');
  for ($i = 0; $i < $#headers; $i+=2) {
      print "$headers[$i] = " . $headers[$i+1] . "\n";
  }

  ($page, $response, $headers, $server_cert)
    = get_https3('www.bacus.pt', 443, '/');
  print "$headers\n";

  ($page, $response, $headers_ref)
    = get_https4('www.bacus.pt', 443, '/');
  for $k (sort keys %{$headers_ref}) {
      for $v (@{$$headers_ref{$k}}) {
	  print "$k = $v\n";
      }
  }

All of the above code fragments accomplish the same thing: display all
values of all headers. The API functions ending in "3" return the
headers simply as a scalar string and it is up to the application to
split them up. The functions ending in "4" return a reference to
a hash of arrays (see L<perlref> and L<perllol> if you are
not familiar with complex perl data structures). To access a single value
of such a header hash you would do something like

  print $$headers_ref{COOKIE}[0];

Variants 3 and 4 also allow you to discover the server certificate
in case you would like to store or display it, e.g.

  ($p, $resp, $hdrs, $server_cert) = get_https3('www.bacus.pt', 443, '/');
  if (!defined($server_cert) || ($server_cert == 0)) {
      warn "Subject Name: undefined, Issuer  Name: undefined";
  } else {
      warn 'Subject Name: '
	  . Net::SSLeay::X509_NAME_oneline(
		 Net::SSLeay::X509_get_subject_name($server_cert))
	      . 'Issuer  Name: '
		  . Net::SSLeay::X509_NAME_oneline(
                         Net::SSLeay::X509_get_issuer_name($server_cert));
  }

Beware that this method only allows after the fact verification of
the certificate: by the time C<get_https3()> has returned the https
request has already been sent to the server, whether you decide to
trust it or not. To do the verification correctly you must either
employ the OpenSSL certificate verification framework or use
the lower level API to first connect and verify the certificate
and only then send the http data. See the implementation of C<ds_https3()>
for guidance on how to do this.

=head3 Using client certificates

Secure web communications are encrypted using symmetric crypto keys
exchanged using encryption based on the certificate of the
server. Therefore in all SSL connections the server must have a
certificate. This serves both to authenticate the server to the
clients and to perform the key exchange.

Sometimes it is necessary to authenticate the client as well. Two
options are available: HTTP basic authentication and a client side
certificate. The basic authentication over HTTPS is actually quite
safe because HTTPS guarantees that the password will not travel in
the clear. Never-the-less, problems like easily guessable passwords
remain. The client certificate method involves authentication of the
client at the SSL level using a certificate. For this to work, both the
client and the server have certificates (which typically are
different) and private keys.

The API functions outlined above accept additional arguments that
allow one to supply the client side certificate and key files. The
format of these files is the same as used for server certificates and
the caveat about encrypting private keys applies.

  ($page, $result, %headers) =                                   # 2c
         = get_https('www.bacus.pt', 443, '/protected.html',
	      make_headers(Authorization =>
			   'Basic ' . MIME::Base64::encode("$user:$pass",'')),
	      '', $mime_type6, $path_to_crt7, $path_to_key8);

  ($page, $response, %reply_headers)
	 = post_https('www.bacus.pt', 443, '/foo.cgi',           # 3b
	      make_headers('Authorization' =>
			   'Basic ' . MIME::Base64::encode("$user:$pass",'')),
	      make_form(OK   => '1', name => 'Sampo'),
	      $mime_type6, $path_to_crt7, $path_to_key8);

B<Case 2c (in SYNOPSIS)> demonstrates getting a password protected page that also requires
a client certificate, i.e. it is possible to use both authentication
methods simultaneously.

B<Case 3b (in SYNOPSIS)> is a full blown POST to a secure server that requires both password
authentication and a client certificate, just like in case 2c.

Note: The client will not send a certificate unless the server requests one.
This is typically achieved by setting the verify mode to C<VERIFY_PEER> on the
server:

  Net::SSLeay::set_verify(ssl, Net::SSLeay::VERIFY_PEER, 0);

See C<perldoc ~openssl/doc/ssl/SSL_CTX_set_verify.pod> for a full description.

=head3 Working through a web proxy

=over

=item * set_proxy

=back

C<Net::SSLeay> can use a web proxy to make its connections. You need to
first set the proxy host and port using C<set_proxy()> and then just
use the normal API functions, e.g:

  Net::SSLeay::set_proxy('gateway.myorg.com', 8080);
  ($page) = get_https('www.bacus.pt', 443, '/');

If your proxy requires authentication, you can supply a username and
password as well

  Net::SSLeay::set_proxy('gateway.myorg.com', 8080, 'joe', 'salainen');
  ($page, $result, %headers) =
         = get_https('www.bacus.pt', 443, '/protected.html',
	      make_headers(Authorization =>
			   'Basic ' . MIME::Base64::encode("susie:pass",''))
	      );

This example demonstrates the case where we authenticate to the proxy as
C<"joe"> and to the final web server as C<"susie">. Proxy authentication
requires the C<MIME::Base64> module to work.

=head3 HTTP (without S) API

=over

=item * get_http

=item * post_http

=item * tcpcat

=item * get_httpx

=item * post_httpx

=item * tcpxcat

=back

Over the years it has become clear that it would be convenient to use
the light-weight flavour API of C<Net::SSLeay> for normal HTTP as well (see
C<LWP> for the heavy-weight object-oriented approach). In fact it would be
nice to be able to flip https on and off on the fly. Thus regular HTTP
support was evolved.

  use Net::SSLeay qw(get_http post_http tcpcat
                      get_httpx post_httpx tcpxcat
                      make_headers make_form);

  ($page, $result, %headers)
         = get_http('www.bacus.pt', 443, '/protected.html',
	      make_headers(Authorization =>
			   'Basic ' . MIME::Base64::encode("$user:$pass",''))
	      );

  ($page, $response, %reply_headers)
	 = post_http('www.bacus.pt', 443, '/foo.cgi', '',
		make_form(OK   => '1',
			  name => 'Sampo'
		));

  ($reply, $err) = tcpcat($host, $port, $request);

  ($page, $result, %headers)
         = get_httpx($usessl, 'www.bacus.pt', 443, '/protected.html',
	      make_headers(Authorization =>
			   'Basic ' . MIME::Base64::encode("$user:$pass",''))
	      );

  ($page, $response, %reply_headers)
	 = post_httpx($usessl, 'www.bacus.pt', 443, '/foo.cgi', '',
		make_form(OK   => '1',  name => 'Sampo'	));

  ($reply, $err, $server_cert) = tcpxcat($usessl, $host, $port, $request);

As can be seen, the C<"x"> family of APIs takes as the first argument a flag
which indicates whether SSL is used or not.

=head2 Certificate verification and Certificate Revocation Lists (CRLs)

OpenSSL supports the ability to verify peer certificates. It can also
optionally check the peer certificate against a Certificate Revocation
List (CRL) from the certificates issuer. A CRL is a file, created by
the certificate issuer that lists all the certificates that it
previously signed, but which it now revokes. CRLs are in PEM format.

You can enable C<Net::SSLeay CRL> checking like this:

	    &Net::SSLeay::X509_STORE_set_flags
		(&Net::SSLeay::CTX_get_cert_store($ssl),
		 &Net::SSLeay::X509_V_FLAG_CRL_CHECK);

After setting this flag, if OpenSSL checks a peer's certificate, then
it will attempt to find a CRL for the issuer. It does this by looking
for a specially named file in the search directory specified by
CTX_load_verify_locations.  CRL files are named with the hash of the
issuer's subject name, followed by C<.r0>, C<.r1> etc.  For example
C<ab1331b2.r0>, C<ab1331b2.r1>. It will read all the .r files for the
issuer, and then check for a revocation of the peer certificate in all
of them.  (You can also force it to look in a specific named CRL
file., see below).  You can find out the hash of the issuer subject
name in a CRL with

	openssl crl -in crl.pem -hash -noout

If the peer certificate does not pass the revocation list, or if no
CRL is found, then the handshaking fails with an error.

You can also force OpenSSL to look for CRLs in one or more arbitrarily
named files.

    my $bio = Net::SSLeay::BIO_new_file($crlfilename, 'r');
    my $crl = Net::SSLeay::PEM_read_bio_X509_CRL($bio);
    if ($crl) {
        Net::SSLeay::X509_STORE_add_crl(
	     Net::SSLeay::CTX_get_cert_store($ssl, $crl)
	);
    } else {
        error reading CRL....
    }

Usually the URLs where you can download the CRLs is contained in the certificate
itself and you can extract them with

    my @url = Net::SSLeay::P_X509_get_crl_distribution_points($cert)

But there is no automatic downloading of the CRLs and often these CRLs are too
huge to just download them to verify a single certificate.
Also, these CRLs are often in DER format which you need to convert to PEM before
you can use it:

    openssl crl -in crl.der -inform der -out crl.pem

So as an alternative for faster and timely revocation checks you better use
the Online Status Revocation Protocol (OCSP).

=head2 Certificate verification and Online Status Revocation Protocol (OCSP)

While checking for revoked certificates is possible and fast with Certificate
Revocation Lists, you need to download the complete and often huge list before
you can verify a single certificate.

A faster way is to ask the CA to check the revocation of just a single or a few
certificates using OCSP. Basically you generate for each certificate an
OCSP_CERTID based on the certificate itself and its issuer, put the ids
togetether into an OCSP_REQUEST and send the request to the URL given in the
certificate.

As a result you get back an OCSP_RESPONSE and need to check the status of the
response, check that it is valid (e.g. signed by the CA) and finally extract the
information about each OCSP_CERTID to find out if the certificate is still valid
or got revoked.

With Net::SSLeay this can be done like this:

    # get id(s) for given certs, like from get_peer_certificate
    # or get_peer_cert_chain. This will croak if
    # - one tries to make an OCSP_CERTID for a self-signed certificate
    # - the issuer of the certificate cannot be found in the SSL objects
    #   store, nor in the current certificate chain
    my $cert = Net::SSLeay::get_peer_certificate($ssl);
    my $id = eval { Net::SSLeay::OCSP_cert2ids($ssl,$cert) };
    die "failed to make OCSP_CERTID: $@" if $@;

    # create OCSP_REQUEST from id(s)
    # Multiple can be put into the same request, if the same OCSP responder
    # is responsible for them.
    my $req = Net::SSLeay::OCSP_ids2req($id);

    # determine URI of OCSP responder
    my $uri = Net::SSLeay::P_X509_get_ocsp_uri($cert);

    # Send stringified OCSP_REQUEST with POST to $uri.
    # We can ignore certificate verification for https, because the OCSP
    # response itself is signed.
    my $ua = HTTP::Tiny->new(verify_SSL => 0);
    my $res = $ua->request( 'POST',$uri, {
	headers => { 'Content-type' => 'application/ocsp-request' },
	content => Net::SSLeay::i2d_OCSP_REQUEST($req)
    });
    my $content = $res && $res->{success} && $res->{content}
	or die "query failed";

    # Extract OCSP_RESPONSE.
    # this will croak if the string is not an OCSP_RESPONSE
    my $resp = eval { Net::SSLeay::d2i_OCSP_RESPONSE($content) };

    # Check status of response.
    my $status = Net::SSLeay::OCSP_response_status($resp);
    if ($status != Net::SSLeay::OCSP_RESPONSE_STATUS_SUCCESSFUL())
	die "OCSP response failed: ".
	    Net::SSLeay::OCSP_response_status_str($status);
    }

    # Verify signature of response and if nonce matches request.
    # This will croak if there is a nonce in the response, but it does not match
    # the request. It will return false if the signature could not be verified,
    # in which case details can be retrieved with Net::SSLeay::ERR_get_error.
    # It will not complain if the response does not contain a nonce, which is
    # usually the case with pre-signed responses.
    if ( ! eval { Net::SSLeay::OCSP_response_verify($ssl,$resp,$req) }) {
	die "OCSP response verification failed";
    }

    # Extract information from OCSP_RESPONSE for each of the ids.

    # If called in scalar context it will return the time (as time_t), when the
    # next update is due (minimum of all successful responses inside $resp). It
    # will croak on the following problems:
    # - response is expired or not yet valid
    # - no response for given OCSP_CERTID
    # - certificate status is not good (e.g. revoked or unknown)
    if ( my $nextupd = eval { Net::SSLeay::OCSP_response_results($resp,$id) }) {
	warn "certificate is valid, next update in ".
	    ($nextupd-time())." seconds\n";
    } else {
	die "certificate is not valid: $@";
    }

    # But in array context it will return detailed information about each given
    # OCSP_CERTID instead croaking on errors:
    # if no @ids are given it will return information about all single responses
    # in the OCSP_RESPONSE
    my @results = Net::SSLeay::OCSP_response_results($resp,@ids);
    for my $r (@results) {
	print Dumper($r);
	# @results are in the same order as the @ids and contain:
	# $r->[0] - OCSP_CERTID
	# $r->[1] - undef if no error (certificate good) OR error message as string
	# $r->[2] - hash with details:
	#   thisUpdate - time_t of this single response
	#   nextUpdate - time_t when update is expected
	#   statusType - integer:
	#      V_OCSP_CERTSTATUS_GOOD(0)
	#      V_OCSP_CERTSTATUS_REVOKED(1)
	#      V_OCSP_CERTSTATUS_UNKNOWN(2)
	#   revocationTime - time_t (only if revoked)
	#   revocationReason - integer (only if revoked)
	#   revocationReason_str - reason as string (only if revoked)
    }

To further speed up certificate revocation checking one can use a TLS extension
to instruct the server to staple the OCSP response:

    # set TLS extension before doing SSL_connect
    Net::SSLeay::set_tlsext_status_type($ssl,
	Net::SSLeay::TLSEXT_STATUSTYPE_ocsp());

    # setup callback to verify OCSP response
    my $cert_valid = undef;
    Net::SSLeay::CTX_set_tlsext_status_cb($context,sub {
	my ($ssl,$resp) = @_;
	if (!$resp) {
	    # Lots of servers don't return an OCSP response.
	    # In this case we must check the OCSP status outside the SSL
	    # handshake.
	    warn "server did not return stapled OCSP response\n";
	    return 1;
	}
	# verify status
	my $status = Net::SSLeay::OCSP_response_status($resp);
	if ($status != Net::SSLeay::OCSP_RESPONSE_STATUS_SUCCESSFUL()) {
	    warn "OCSP response failure: $status\n";
	    return 1;
	}
	# verify signature - we have no OCSP_REQUEST here to check nonce
	if (!eval { Net::SSLeay::OCSP_response_verify($ssl,$resp) }) {
	    warn "OCSP response verify failed\n";
	    return 1;
	}
	# check if the certificate is valid
	# we should check here against the peer_certificate
	my $cert = Net::SSLeay::get_peer_certificate();
	my $certid = eval { Net::SSLeay::OCSP_cert2ids($ssl,$cert) } or do {
	    warn "cannot get certid from cert: $@";
	    $cert_valid = -1;
	    return 1;
	};

	if ( $nextupd = eval {
	    Net::SSLeay::OCSP_response_results($resp,$certid) }) {
	    warn "certificate not revoked\n";
	    $cert_valid = 1;
	} else {
	    warn "certificate not valid: $@";
	    $cert_valid = 0;
	}
    });

    # do SSL handshake here
    ....
    # check if certificate revocation was checked already
    if ( ! defined $cert_valid) {
	# check revocation outside of SSL handshake by asking OCSP responder
	...
    } elsif ( ! $cert_valid ) {
	die "certificate not valid - closing SSL connection";
    } elsif ( $cert_valid<0 ) {
	die "cannot verify certificate revocation - self-signed ?";
    } else {
	# everything fine
	...
    }


=head2 Using Net::SSLeay in multi-threaded applications

B<IMPORTANT: versions 1.42 or earlier are not thread-safe!>

Net::SSLeay module implements all necessary stuff to be ready for multi-threaded
environment - it requires openssl-0.9.7 or newer. The implementation fully follows thread safety related requirements
of openssl library(see L<http://www.openssl.org/docs/crypto/threads.html|http://www.openssl.org/docs/crypto/threads.html>).

If you are about to use Net::SSLeay (or any other module based on Net::SSLeay) in multi-threaded
perl application it is recommended to follow this best-practice:

=head3 Initialization

Load and initialize Net::SSLeay module in the main thread:

    use threads;
    use Net::SSLeay;

    Net::SSLeay::load_error_strings();
    Net::SSLeay::SSLeay_add_ssl_algorithms();
    Net::SSLeay::randomize();

    sub do_master_job {
      #... call whatever from Net::SSLeay
    }

    sub do_worker_job {
      #... call whatever from Net::SSLeay
    }

    #start threads
    my $master  = threads->new(\&do_master_job, 'param1', 'param2');
    my @workers = threads->new(\&do_worker_job, 'arg1', 'arg2') for (1..10);

    #waiting for all threads to finish
    $_->join() for (threads->list);

NOTE: Openssl's C<int SSL_library_init(void)> function (which is also aliased as
C<SSLeay_add_ssl_algorithms>, C<OpenSSL_add_ssl_algorithms> and C<add_ssl_algorithms>)
is not re-entrant and multiple calls can cause a crash in threaded application.
Net::SSLeay implements flags preventing repeated calls to this function,
therefore even multiple initialization via Net::SSLeay::SSLeay_add_ssl_algorithms()
should work without trouble.

=head3 Using callbacks

Do not use callbacks across threads (the module blocks cross-thread callback operations
and throws a warning). Always do the callback setup, callback use and callback destruction
within the same thread.

=head3 Using openssl elements

All openssl elements (X509, SSL_CTX, ...) can be directly passed between threads.

    use threads;
    use Net::SSLeay;

    Net::SSLeay::load_error_strings();
    Net::SSLeay::SSLeay_add_ssl_algorithms();
    Net::SSLeay::randomize();

    sub do_job {
      my $context = shift;
      Net::SSLeay::CTX_set_default_passwd_cb($context, sub { "secret" });
      #...
    }

    my $c = Net::SSLeay::CTX_new();
    threads->create(\&do_job, $c);

Or:

    use threads;
    use Net::SSLeay;

    my $context; #does not need to be 'shared'

    Net::SSLeay::load_error_strings();
    Net::SSLeay::SSLeay_add_ssl_algorithms();
    Net::SSLeay::randomize();

    sub do_job {
      Net::SSLeay::CTX_set_default_passwd_cb($context, sub { "secret" });
      #...
    }

    $context = Net::SSLeay::CTX_new();
    threads->create(\&do_job);


=head3 Using other perl modules based on Net::SSLeay

It should be fine to use any other module based on L<Net::SSLeay> (like L<IO::Socket::SSL>)
in multi-threaded applications. It is generally recommended to do any global initialization
of such a module in the main thread before calling C<< threads->new(..) >> or
C<< threads->create(..) >> but it might differ module by module.

To be safe you can load and init Net::SSLeay explicitly in the main thread:

    use Net::SSLeay;
    use Other::SSLeay::Based::Module;

    Net::SSLeay::load_error_strings();
    Net::SSLeay::SSLeay_add_ssl_algorithms();
    Net::SSLeay::randomize();

Or even safer:

    use Net::SSLeay;
    use Other::SSLeay::Based::Module;

    BEGIN {
      Net::SSLeay::load_error_strings();
      Net::SSLeay::SSLeay_add_ssl_algorithms();
      Net::SSLeay::randomize();
    }

=head3 Combining Net::SSLeay with other modules linked with openssl

B<BEWARE: This might be a big trouble! This is not guaranteed be thread-safe!>

There are many other (XS) modules linked directly to openssl library (like L<Crypt::SSLeay>).

As it is expected that also "another" module will call C<SSLeay_add_ssl_algorithms> at some point
we have again a trouble with multiple openssl initialization by Net::SSLeay and "another" module.

As you can expect Net::SSLeay is not able to avoid multiple initialization of openssl library
called by "another" module, thus you have to handle this on your own (in some cases it might
not be possible at all to avoid this).

=head3 Threading with get_https and friends

The convenience functions get_https, post_https etc all initialize the SSL library by calling
Net::SSLeay::initialize which does the conventional library initialization:

    Net::SSLeay::load_error_strings();
    Net::SSLeay::SSLeay_add_ssl_algorithms();
    Net::SSLeay::randomize();

Net::SSLeay::initialize initializes the SSL library at most once.
You can override the Net::SSLeay::initialize function if you desire
some other type of initialization behaviour by get_https and friends.
You can call Net::SSLeay::initialize from your own code if you desire this conventional library initialization.

=head2 Convenience routines

To be used with Low level API

    Net::SSLeay::randomize($rn_seed_file,$additional_seed);
    Net::SSLeay::set_cert_and_key($ctx, $cert_path, $key_path);
    $cert = Net::SSLeay::dump_peer_certificate($ssl);
    Net::SSLeay::ssl_write_all($ssl, $message) or die "ssl write failure";
    $got = Net::SSLeay::ssl_read_all($ssl) or die "ssl read failure";

    $got = Net::SSLeay::ssl_read_CRLF($ssl [, $max_length]);
    $got = Net::SSLeay::ssl_read_until($ssl [, $delimit [, $max_length]]);
    Net::SSLeay::ssl_write_CRLF($ssl, $message);

=over

=item * randomize

seeds the openssl PRNG with C</dev/urandom> (see the top of C<SSLeay.pm>
for how to change or configure this) and optionally with user provided
data. It is very important to properly seed your random numbers, so
do not forget to call this. The high level API functions automatically
call C<randomize()> so it is not needed with them. See also caveats.

=item * set_cert_and_key

takes two file names as arguments and sets
the certificate and private key to those. This can be used to
set either server certificates or client certificates.

=item * dump_peer_certificate

allows you to get a plaintext description of the
certificate the peer (usually the server) presented to us.

=item * ssl_read_all

see ssl_write_all (below)

=item * ssl_write_all

C<ssl_read_all()> and C<ssl_write_all()> provide true blocking semantics for
these operations (see limitation, below, for explanation). These are
much preferred to the low level API equivalents (which implement BSD
blocking semantics). The message argument to C<ssl_write_all()> can be
a reference. This is helpful to avoid unnecessary copying when writing
something big, e.g:

    $data = 'A' x 1000000000;
    Net::SSLeay::ssl_write_all($ssl, \$data) or die "ssl write failed";

=item * ssl_read_CRLF

uses C<ssl_read_all()> to read in a line terminated with a
carriage return followed by a linefeed (CRLF).  The CRLF is included in
the returned scalar.

=item * ssl_read_until

uses C<ssl_read_all()> to read from the SSL input
stream until it encounters a programmer specified delimiter.
If the delimiter is undefined, C<$/> is used.  If C<$/> is undefined,
C<\n> is used.  One can optionally set a maximum length of bytes to read
from the SSL input stream.

=item * ssl_write_CRLF

writes C<$message> and appends CRLF to the SSL output stream.

=back

=head2 Initialization

In order to use the low level API you should start your programs with
the following incantation:

	use Net::SSLeay qw(die_now die_if_ssl_error);
	Net::SSLeay::load_error_strings();
	Net::SSLeay::SSLeay_add_ssl_algorithms();    # Important!
        Net::SSLeay::ENGINE_load_builtin_engines();  # If you want built-in engines
        Net::SSLeay::ENGINE_register_all_complete(); # If you want built-in engines
        Net::SSLeay::randomize();

=head2 Error handling functions

I can not emphasize the need to check for error enough. Use these
functions even in the most simple programs, they will reduce debugging
time greatly. Do not ask questions on the mailing list without having
first sprinkled these in your code.

=over

=item * die_now

=item * die_if_ssl_error

C<die_now()> and C<die_if_ssl_error()> are used to conveniently print the SSLeay error
stack when something goes wrong:

	Net::SSLeay::connect($ssl) or die_now("Failed SSL connect ($!)");


	Net::SSLeay::write($ssl, "foo") or die_if_ssl_error("SSL write ($!)");

=item * print_errs

You can also use C<Net::SSLeay::print_errs()> to dump the error stack without
exiting the program. As can be seen, your code becomes much more readable
if you import the error reporting functions into your main name space.

=back

=head2 Sockets

Perl uses file handles for all I/O. While SSLeay has a quite flexible BIO
mechanism and perl has an evolved PerlIO mechanism, this module still
sticks to using file descriptors. Thus to attach SSLeay to a socket you
should use C<fileno()> to extract the underlying file descriptor:

    Net::SSLeay::set_fd($ssl, fileno(S));   # Must use fileno

You should also set C<$|> to 1 to eliminate STDIO buffering so you do not
get confused if you use perl I/O functions to manipulate your socket
handle.

If you need to C<select(2)> on the socket, go right ahead, but be warned
that OpenSSL does some internal buffering so SSL_read does not always
return data even if the socket selected for reading (just keep on
selecting and trying to read). C<Net::SSLeay> is no different from the
C language OpenSSL in this respect.

=head2 Callbacks

You can establish a per-context verify callback function something like this:

	sub verify {
	    my ($ok, $x509_store_ctx) = @_;
	    print "Verifying certificate...\n";
		...
	    return $ok;
	}

It is used like this:

	Net::SSLeay::set_verify ($ssl, Net::SSLeay::VERIFY_PEER, \&verify);

Per-context callbacks for decrypting private keys are implemented.

        Net::SSLeay::CTX_set_default_passwd_cb($ctx, sub { "top-secret" });
        Net::SSLeay::CTX_use_PrivateKey_file($ctx, "key.pem",
					     Net::SSLeay::FILETYPE_PEM)
            or die "Error reading private key";
        Net::SSLeay::CTX_set_default_passwd_cb($ctx, undef);

If Hello Extensions are supported by your OpenSSL,
a session secret callback can be set up to be called when a session secret is set
by openssl.

Establish it like this:
    Net::SSLeay::set_session_secret_cb($ssl, \&session_secret_cb, $somedata);

It will be called like this:

    sub session_secret_cb
    {
        my ($secret, \@cipherlist, \$preferredcipher, $somedata) = @_;
    }


No other callbacks are implemented. You do not need to use any
callback for simple (i.e. normal) cases where the SSLeay built-in
verify mechanism satisfies your needs.

It is required to reset these callbacks to undef immediately after use to prevent
memory leaks, thread safety problems and crashes on exit that
can occur if different threads set different callbacks.

If you want to use callback stuff, see examples/callback.pl! It's the
only one I am able to make work reliably.

=head2 Low level API

In addition to the high level functions outlined above, this module
contains straight-forward access to CRYPTO and SSL parts of OpenSSL C API.

See the C<*.h> headers from OpenSSL C distribution for a list of low level
SSLeay functions to call (check SSLeay.xs to see if some function has been
implemented). The module strips the initial C<"SSL_"> off of the SSLeay names.
Generally you should use C<Net::SSLeay::> in its place.

Note that some functions are prefixed with C<"P_"> - these are very close to
the original API however contain some kind of a wrapper making its interface
more perl friendly.

For example:

In C:

	#include <ssl.h>

	err = SSL_set_verify (ssl, SSL_VERIFY_CLIENT_ONCE,
				   &your_call_back_here);

In Perl:

	use Net::SSLeay;

	$err = Net::SSLeay::set_verify ($ssl,
					Net::SSLeay::VERIFY_CLIENT_ONCE,
					\&your_call_back_here);

If the function does not start with C<SSL_> you should use the full
function name, e.g.:

	$err = Net::SSLeay::ERR_get_error;

The following new functions behave in perlish way:

	$got = Net::SSLeay::read($ssl);
                                    # Performs SSL_read, but returns $got
                                    # resized according to data received.
                                    # Returns undef on failure.

	Net::SSLeay::write($ssl, $foo) || die;
                                    # Performs SSL_write, but automatically
                                    # figures out the size of $foo

=head3 Low level API: Version related functions

=over

=item * SSLeay

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before

Gives version number (numeric) of underlaying openssl library.

 my $ver_number = Net::SSLeay::SSLeay();
 # returns: the number identifying the openssl release
 #
 # 0x00903100 => openssl-0.9.3
 # 0x00904100 => openssl-0.9.4
 # 0x00905100 => openssl-0.9.5
 # 0x0090600f => openssl-0.9.6
 # 0x0090601f => openssl-0.9.6a
 # 0x0090602f => openssl-0.9.6b
 # ...
 # 0x009060df => openssl-0.9.6m
 # 0x0090700f => openssl-0.9.7
 # 0x0090701f => openssl-0.9.7a
 # 0x0090702f => openssl-0.9.7b
 # ...
 # 0x009070df => openssl-0.9.7m
 # 0x0090800f => openssl-0.9.8
 # 0x0090801f => openssl-0.9.8a
 # 0x0090802f => openssl-0.9.8b
 # ...
 # 0x0090814f => openssl-0.9.8t
 # 0x1000000f => openssl-1.0.0
 # 0x1000004f => openssl-1.0.0d
 # 0x1000007f => openssl-1.0.0g

You can use it like this:

  if (Net::SSLeay::SSLeay() < 0x0090800f) {
    die "you need openssl-0.9.8 or higher";
  }

=item * SSLeay_version

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before

Gives version number (string) of underlaying openssl library.

 my $ver_string = Net::SSLeay::SSLeay_version($type);
 # $type
 #   SSLEAY_VERSION  - e.g. 'OpenSSL 1.0.0d 8 Feb 2011'
 #   SSLEAY_CFLAGS   - e.g. 'compiler: gcc -D_WINDLL -DOPENSSL_USE_APPLINK .....'
 #   SSLEAY_BUILT_ON - e.g. 'built on: Fri May  6 00:00:46 GMT 2011'
 #   SSLEAY_PLATFORM - e.g. 'platform: mingw'
 #   SSLEAY_DIR      - e.g. 'OPENSSLDIR: "z:/...."'
 #
 # returns: string

 Net::SSLeay::SSLeay_version();
 #is equivalent to
 Net::SSLeay::SSLeay_version(SSLEAY_VERSION);

Check openssl doc L<https://www.openssl.org/docs/man1.0.2/crypto/SSLeay_version.html|https://www.openssl.org/docs/man1.0.2/crypto/SSLeay_version.html>

=item * OpenSSL_version_num

B<COMPATIBILITY:> not available in Net-SSLeay-1.82 and before; requires at least OpenSSL 1.1.0

Gives version number (numeric) of underlaying openssl library. See L</SSLeay> for interpreting the result.

 my $ver_number = Net::SSLeay::OpenSSL_version_num();
 # returns: the number identifying the openssl release

=item * OpenSSL_version

B<COMPATIBILITY:> not available in Net-SSLeay-1.82 and before; requires at least OpenSSL 1.1.0

Gives version number (string) of underlaying openssl library.

 my $ver_string = Net::SSLeay::OpenSSL_version($t);
 # $t
 #   OPENSSL_VERSION     - e.g. 'OpenSSL 1.1.0g  2 Nov 2017'
 #   OPENSSL_CFLAGS      - e.g. 'compiler: cc -DDSO_DLFCN -DHAVE_DLFCN_H .....'
 #   OPENSSL_BUILT_ON    - e.g. 'built on: reproducible build, date unspecified'
 #   OPENSSL_PLATFORM    - e.g. 'platform: darwin64-x86_64-cc'
 #   OPENSSL_DIR         - e.g. 'OPENSSLDIR: "/opt/openssl-1.1.0g"'
 #   OPENSSL_ENGINES_DIR - e.g. 'ENGINESDIR: "/opt/openssl-1.1.0g/lib/engines-1.1"'
 #
 # returns: string

 Net::SSLeay::OpenSSL_version();
 #is equivalent to
 Net::SSLeay::OpenSSL_version(OPENSSL_VERSION);

Check openssl doc L<https://www.openssl.org/docs/crypto/OpenSSL_version.html|https://www.openssl.org/docs/crypto/OpenSSL_version.html>

=back

=head3 Low level API: Initialization related functions

=over

=item * library_init

Initialize SSL library by registering algorithms.

 my $rv = Net::SSLeay::library_init();

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_library_init.html|http://www.openssl.org/docs/ssl/SSL_library_init.html>

While the original function from OpenSSL always returns 1, Net::SSLeay adds a
wrapper around it to make sure that the OpenSSL function is only called once.
Thus the function will return 1 if initialization was done and 0 if not, i.e. if
initialization was done already before.

=item * add_ssl_algorithms

The alias for L</library_init>

 Net::SSLeay::add_ssl_algorithms();

=item * OpenSSL_add_ssl_algorithms

The alias for L</library_init>

 Net::SSLeay::OpenSSL_add_ssl_algorithms();

=item * SSLeay_add_ssl_algorithms

The alias for L</library_init>

 Net::SSLeay::SSLeay_add_ssl_algorithms();

=item * load_error_strings

Registers the error strings for all libcrypto + libssl related functions.

 Net::SSLeay::load_error_strings();
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/crypto/ERR_load_crypto_strings.html|http://www.openssl.org/docs/crypto/ERR_load_crypto_strings.html>

=item * ERR_load_crypto_strings

Registers the error strings for all libcrypto functions. No need to call this function if you have already called L</load_error_strings>.

 Net::SSLeay::ERR_load_crypto_strings();
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/crypto/ERR_load_crypto_strings.html|http://www.openssl.org/docs/crypto/ERR_load_crypto_strings.html>

=item * ERR_load_RAND_strings

Registers the error strings for RAND related functions. No need to call this function if you have already called L</load_error_strings>.

 Net::SSLeay::ERR_load_RAND_strings();
 #
 # returns: no return value

=item * ERR_load_SSL_strings

Registers the error strings for SSL related functions. No need to call this function if you have already called L</load_error_strings>.

 Net::SSLeay::ERR_load_SSL_strings();
 #
 # returns: no return value

=item * OpenSSL_add_all_algorithms

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Add algorithms to internal table.

 Net::SSLeay::OpenSSL_add_all_algorithms();
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/crypto/OpenSSL_add_all_algorithms.html|http://www.openssl.org/docs/crypto/OpenSSL_add_all_algorithms.html>

=item * OPENSSL_add_all_algorithms_conf

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Similar to L</OpenSSL_add_all_algorithms> - will ALWAYS load the config file

 Net::SSLeay::OPENSSL_add_all_algorithms_conf();
 #
 # returns: no return value

=item * OPENSSL_add_all_algorithms_noconf

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Similar to L</OpenSSL_add_all_algorithms> - will NEVER load the config file

 Net::SSLeay::OPENSSL_add_all_algorithms_noconf();
 #
 # returns: no return value

=back

=head3 Low level API: ERR_* and SSL_alert_* related functions

B<NOTE:> Please note that SSL_alert_* function have "SSL_" part stripped from their names.

=over

=item * ERR_clear_error

Clear the error queue.

 Net::SSLeay::ERR_clear_error();
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/crypto/ERR_clear_error.html|http://www.openssl.org/docs/crypto/ERR_clear_error.html>

=item * ERR_error_string

Generates a human-readable string representing the error code $error.

 my $rv = Net::SSLeay::ERR_error_string($error);
 # $error - (unsigned integer) error code
 #
 # returns: string

Check openssl doc L<http://www.openssl.org/docs/crypto/ERR_error_string.html|http://www.openssl.org/docs/crypto/ERR_error_string.html>

=item * ERR_get_error

Returns the earliest error code from the thread's error queue and removes the entry.
This function can be called repeatedly until there are no more error codes to return.

 my $rv = Net::SSLeay::ERR_get_error();
 #
 # returns: (unsigned integer) error code

Check openssl doc L<http://www.openssl.org/docs/crypto/ERR_get_error.html|http://www.openssl.org/docs/crypto/ERR_get_error.html>

=item * ERR_peek_error

Returns the earliest error code from the thread's error queue without modifying it.

 my $rv = Net::SSLeay::ERR_peek_error();
 #
 # returns: (unsigned integer) error code

Check openssl doc L<http://www.openssl.org/docs/crypto/ERR_get_error.html|http://www.openssl.org/docs/crypto/ERR_get_error.html>

=item * ERR_put_error

Adds an error code to the thread's error queue. It signals that the error of $reason
code reason occurred in function $func of library $lib, in line number $line of $file.

 Net::SSLeay::ERR_put_error($lib, $func, $reason, $file, $line);
 # $lib - (integer) library id (check openssl/err.h for constants e.g. ERR_LIB_SSL)
 # $func - (integer) function id (check openssl/ssl.h for constants e.g. SSL_F_SSL23_READ)
 # $reason - (integer) reason id (check openssl/ssl.h for constants e.g. SSL_R_SSL_HANDSHAKE_FAILURE)
 # $file - (string) file name
 # $line - (integer) line number in $file
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/crypto/ERR_put_error.html|http://www.openssl.org/docs/crypto/ERR_put_error.html>
and L<http://www.openssl.org/docs/crypto/err.html|http://www.openssl.org/docs/crypto/err.html>

=item * alert_desc_string

Returns a two letter string as a short form describing the reason of the alert specified by value.

 my $rv = Net::SSLeay::alert_desc_string($value);
 # $value - (integer) allert id (check openssl/ssl.h for SSL3_AD_* and TLS1_AD_* constants)
 #
 # returns: description string (2 letters)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_alert_type_string.html|http://www.openssl.org/docs/ssl/SSL_alert_type_string.html>

=item * alert_desc_string_long

Returns a string describing the reason of the alert specified by value.

 my $rv = Net::SSLeay::alert_desc_string_long($value);
 # $value - (integer) allert id (check openssl/ssl.h for SSL3_AD_* and TLS1_AD_* constants)
 #
 # returns: description string

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_alert_type_string.html|http://www.openssl.org/docs/ssl/SSL_alert_type_string.html>

=item * alert_type_string

Returns a one letter string indicating the type of the alert specified by value.

 my $rv = Net::SSLeay::alert_type_string($value);
 # $value - (integer) allert id (check openssl/ssl.h for SSL3_AD_* and TLS1_AD_* constants)
 #
 # returns: string (1 letter)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_alert_type_string.html|http://www.openssl.org/docs/ssl/SSL_alert_type_string.html>

=item * alert_type_string_long

Returns a string indicating the type of the alert specified by value.

 my $rv = Net::SSLeay::alert_type_string_long($value);
 # $value - (integer) allert id (check openssl/ssl.h for SSL3_AD_* and TLS1_AD_* constants)
 #
 # returns: string

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_alert_type_string.html|http://www.openssl.org/docs/ssl/SSL_alert_type_string.html>

=back

=head3 Low level API: SSL_METHOD_* related functions

=over

=item * SSLv23_method, SSLv23_server_method and SSLv23_client_method

B<COMPATIBILITY:> not available in Net-SSLeay-1.82 and before.

Returns SSL_METHOD structure corresponding to general-purpose version-flexible TLS method, the return value can be later used as a param of L</CTX_new_with_method>.

B<NOTE:> Consider using TLS_method, TLS_server_method or TLS_client_method with new code.

 my $rv = Net::SSLeay::SSLv2_method();
 #
 # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

=item * SSLv2_method

Returns SSL_METHOD structure corresponding to SSLv2 method, the return value can be later used as a param of L</CTX_new_with_method>. Only available where supported by the underlying openssl.

 my $rv = Net::SSLeay::SSLv2_method();
 #
 # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

=item * SSLv3_method

Returns SSL_METHOD structure corresponding to SSLv3 method, the return value can be later used as a param of L</CTX_new_with_method>.

 my $rv = Net::SSLeay::SSLv3_method();
 #
 # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_new.html|http://www.openssl.org/docs/ssl/SSL_CTX_new.html>

=item * TLSv1_method, TLSv1_server_method and TLSv1_client_method

B<COMPATIBILITY:> Server and client methods not available in Net-SSLeay-1.82 and before.

Returns SSL_METHOD structure corresponding to TLSv1 method, the return value can be later used as a param of L</CTX_new_with_method>.

 my $rv = Net::SSLeay::TLSv1_method();
 #
 # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_new.html|http://www.openssl.org/docs/ssl/SSL_CTX_new.html>

=item * TLSv1_1_method, TLSv1_1_server_method and TLSv1_1_client_method

B<COMPATIBILITY:> Server and client methods not available in Net-SSLeay-1.82 and before.

Returns SSL_METHOD structure corresponding to TLSv1_1 method, the return value can be later used as a param of L</CTX_new_with_method>. Only available where supported by the underlying openssl.

 my $rv = Net::SSLeay::TLSv1_1_method();
 #
 # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_new.html|http://www.openssl.org/docs/ssl/SSL_CTX_new.html>

=item * TLSv1_2_method, TLSv1_2_server_method and TLSv1_2_client_method

B<COMPATIBILITY:> Server and client methods not available in Net-SSLeay-1.82 and before.

Returns SSL_METHOD structure corresponding to TLSv1_2 method, the return value can be later used as a param of L</CTX_new_with_method>. Only available where supported by the underlying openssl.

 my $rv = Net::SSLeay::TLSv1_2_method();
 #
 # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_new.html|http://www.openssl.org/docs/ssl/SSL_CTX_new.html>

=item * TLS_method, TLS_server_method and TLS_client_method

B<COMPATIBILITY:> Not available in Net-SSLeay-1.82 and before.

Returns SSL_METHOD structure corresponding to general-purpose version-flexible TLS method, the return value can be later used as a param of L</CTX_new_with_method>. Only available where supported by the underlying openssl.

 my $rv = Net::SSLeay::TLS_method();
 #
 # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_new.html|http://www.openssl.org/docs/ssl/SSL_CTX_new.html>

=back

=head3 Low level API: ENGINE_* related functions

=over

=item * ENGINE_load_builtin_engines

B<COMPATIBILITY:> Requires an OpenSSL build with dynamic engine loading support.

Load all bundled ENGINEs into memory and make them visible.

 Net::SSLeay::ENGINE_load_builtin_engines();
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/crypto/engine.html|http://www.openssl.org/docs/crypto/engine.html>

=item * ENGINE_register_all_complete

B<COMPATIBILITY:> Requires an OpenSSL build with dynamic engine loading support.

Register all loaded ENGINEs for every algorithm they collectively implement.

 Net::SSLeay::ENGINE_register_all_complete();
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/crypto/engine.html|http://www.openssl.org/docs/crypto/engine.html>

=item * ENGINE_set_default

B<COMPATIBILITY:> Requires an OpenSSL build with dynamic engine loading support.

Set default engine to $e + set its flags to $flags.

 my $rv = Net::SSLeay::ENGINE_set_default($e, $flags);
 # $e - value corresponding to openssl's ENGINE structure
 # $flags - (integer) engine flags
 #          flags value can be made by bitwise "OR"ing:
 #          0x0001 - ENGINE_METHOD_RSA
 #          0x0002 - ENGINE_METHOD_DSA
 #          0x0004 - ENGINE_METHOD_DH
 #          0x0008 - ENGINE_METHOD_RAND
 #          0x0010 - ENGINE_METHOD_ECDH
 #          0x0020 - ENGINE_METHOD_ECDSA
 #          0x0040 - ENGINE_METHOD_CIPHERS
 #          0x0080 - ENGINE_METHOD_DIGESTS
 #          0x0100 - ENGINE_METHOD_STORE
 #          0x0200 - ENGINE_METHOD_PKEY_METHS
 #          0x0400 - ENGINE_METHOD_PKEY_ASN1_METHS
 #          Obvious all-or-nothing cases:
 #          0xFFFF - ENGINE_METHOD_ALL
 #          0x0000 - ENGINE_METHOD_NONE
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/crypto/engine.html|http://www.openssl.org/docs/crypto/engine.html>

=item * ENGINE_by_id

Get ENGINE by its identification $id.

B<COMPATIBILITY:> Requires an OpenSSL build with dynamic engine loading support.

 my $rv = Net::SSLeay::ENGINE_by_id($id);
 # $id - (string) engine identification e.g. "dynamic"
 #
 # returns: value corresponding to openssl's ENGINE structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/crypto/engine.html|http://www.openssl.org/docs/crypto/engine.html>

=back

=head3 Low level API: EVP_PKEY_* related functions

=over

=item * EVP_PKEY_copy_parameters

Copies the parameters from key $from to key $to.

 my $rv = Net::SSLeay::EVP_PKEY_copy_parameters($to, $from);
 # $to - value corresponding to openssl's EVP_PKEY structure
 # $from - value corresponding to openssl's EVP_PKEY structure
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/crypto/EVP_PKEY_cmp.html|http://www.openssl.org/docs/crypto/EVP_PKEY_cmp.html>

=item * EVP_PKEY_new

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Creates a new EVP_PKEY structure.

 my $rv = Net::SSLeay::EVP_PKEY_new();
 #
 # returns: value corresponding to openssl's EVP_PKEY structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/crypto/EVP_PKEY_new.html|http://www.openssl.org/docs/crypto/EVP_PKEY_new.html>

=item * EVP_PKEY_free

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Free an allocated EVP_PKEY structure.

 Net::SSLeay::EVP_PKEY_free($pkey);
 # $pkey - value corresponding to openssl's EVP_PKEY structure
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/crypto/EVP_PKEY_new.html|http://www.openssl.org/docs/crypto/EVP_PKEY_new.html>

=item * EVP_PKEY_assign_RSA

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Set the key referenced by $pkey to $key

B<NOTE:> No reference counter will be increased, i.e. $key will be freed if
$pkey is freed.

 my $rv = Net::SSLeay::EVP_PKEY_assign_RSA($pkey, $key);
 # $pkey - value corresponding to openssl's EVP_PKEY structure
 # $key - value corresponding to openssl's RSA structure
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/crypto/EVP_PKEY_assign_RSA.html|http://www.openssl.org/docs/crypto/EVP_PKEY_assign_RSA.html>
 
=item * EVP_PKEY_assign_EC_KEY

B<COMPATIBILITY:> not available in Net-SSLeay-1.74 and before

Set the key referenced by $pkey to $key

B<NOTE:> No reference counter will be increased, i.e. $key will be freed if
$pkey is freed.

 my $rv = Net::SSLeay::EVP_PKEY_assign_EC_KEY($pkey, $key);
 # $pkey - value corresponding to openssl's EVP_PKEY structure
 # $key - value corresponding to openssl's EC_KEY structure
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/crypto/EVP_PKEY_assign_EC_KEY.html|http://www.openssl.org/docs/crypto/EVP_PKEY_assign_EC_KEY.html>

=item * EVP_PKEY_bits

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns the size of the key $pkey in bits.

 my $rv = Net::SSLeay::EVP_PKEY_bits($pkey);
 # $pkey - value corresponding to openssl's EVP_PKEY structure
 #
 # returns: size in bits

=item * EVP_PKEY_size

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns the maximum size of a signature in bytes. The actual signature may be smaller.

 my $rv = Net::SSLeay::EVP_PKEY_size($pkey);
 # $pkey - value corresponding to openssl's EVP_PKEY structure
 #
 # returns: the maximum size in bytes

Check openssl doc L<http://www.openssl.org/docs/crypto/EVP_SignInit.html|http://www.openssl.org/docs/crypto/EVP_SignInit.html>

=item * EVP_PKEY_id

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before; requires at least openssl-1.0.0

Returns $pkey type (integer value of corresponding NID).

 my $rv = Net::SSLeay::EVP_PKEY_id($pkey);
 # $pkey - value corresponding to openssl's EVP_PKEY structure
 #
 # returns: (integer) key type

Example:

 my $pubkey = Net::SSLeay::X509_get_pubkey($x509);
 my $type = Net::SSLeay::EVP_PKEY_id($pubkey);
 print Net::SSLeay::OBJ_nid2sn($type);             #prints e.g. 'rsaEncryption'

=back

=head3 Low level API: PEM_* related functions

Check openssl doc L<http://www.openssl.org/docs/crypto/pem.html|http://www.openssl.org/docs/crypto/pem.html>

=over

=item * PEM_read_bio_X509

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Loads PEM formatted X509 certificate via given BIO structure.

 my $rv = Net::SSLeay::PEM_read_bio_X509($bio);
 # $bio - value corresponding to openssl's BIO structure
 #
 # returns: value corresponding to openssl's X509 structure (0 on failure)

Example:

 my $bio = Net::SSLeay::BIO_new_file($filename, 'r');
 my $x509 = Net::SSLeay::PEM_read_bio_X509($bio);
 Net::SSLeay::BIO_free($bio);

=item * PEM_read_bio_X509_REQ

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Loads PEM formatted X509_REQ object via given BIO structure.

 my $rv = Net::SSLeay::PEM_read_bio_X509_REQ($bio, $x=NULL, $cb=NULL, $u=NULL);
 # $bio - value corresponding to openssl's BIO structure
 #
 # returns: value corresponding to openssl's X509_REQ structure (0 on failure)

Example:

 my $bio = Net::SSLeay::BIO_new_file($filename, 'r');
 my $x509_req = Net::SSLeay::PEM_read_bio_X509_REQ($bio);
 Net::SSLeay::BIO_free($bio);

=item * PEM_read_bio_DHparams

Reads DH structure from BIO.

 my $rv = Net::SSLeay::PEM_read_bio_DHparams($bio);
 # $bio - value corresponding to openssl's BIO structure
 #
 # returns: value corresponding to openssl's DH structure (0 on failure)

=item * PEM_read_bio_X509_CRL

Reads X509_CRL structure from BIO.

 my $rv = Net::SSLeay::PEM_read_bio_X509_CRL($bio);
 # $bio - value corresponding to openssl's BIO structure
 #
 # returns: value corresponding to openssl's X509_CRL structure (0 on failure)

=item * PEM_read_bio_PrivateKey

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Loads PEM formatted private key via given BIO structure.

 my $rv = Net::SSLeay::PEM_read_bio_PrivateKey($bio, $cb, $data);
 # $bio - value corresponding to openssl's BIO structure
 # $cb - reference to perl callback function
 # $data - data that will be passed to callback function (see examples below)
 #
 # returns: value corresponding to openssl's EVP_PKEY structure (0 on failure)

Example:

 my $bio = Net::SSLeay::BIO_new_file($filename, 'r');
 my $privkey = Net::SSLeay::PEM_read_bio_PrivateKey($bio); #ask for password if needed
 Net::SSLeay::BIO_free($bio);

To use password you have the following options:

 $privkey = Net::SSLeay::PEM_read_bio_PrivateKey($bio, \&callback_func); # use callback func for getting password
 $privkey = Net::SSLeay::PEM_read_bio_PrivateKey($bio, \&callback_func, $data); # use callback_func + pass $data to callback_func
 $privkey = Net::SSLeay::PEM_read_bio_PrivateKey($bio, undef, "secret"); # use password "secret"
 $privkey = Net::SSLeay::PEM_read_bio_PrivateKey($bio, undef, "");       # use empty password

Callback function signature:

 sub callback_func {
   my ($max_passwd_size, $rwflag, $data) = @_;
   # $max_passwd_size - maximum size of returned password (longer values will be discarded)
   # $rwflag - indicates whether we are loading (0) or storing (1) - for PEM_read_bio_PrivateKey always 0
   # $data - the data passed to PEM_read_bio_PrivateKey as 3rd parameter

   return "secret";
 }

=item * PEM_X509_INFO_read_bio

Reads a BIO containing a PEM formatted file into a STACK_OF(X509_INFO) structure.

 my $rv = Net::SSLeay::PEM_X509_INFO_read_bio($bio);
 # $bio - value corresponding to openssl's BIO structure
 #
 # returns: value corresponding to openssl's STACK_OF(X509_INFO) structure.

Example:

 my $bio = Net::SSLeay::BIO_new_file($filename, 'r');
 my $sk_x509_info = Net::SSLeay::PEM_X509_INFO_read_bio($bio);
 Net::SSLeay::BIO_free($bio);

=item * PEM_get_string_X509

B<NOTE:> Does not exactly correspond to any low level API function

Converts/exports X509 certificate to string (PEM format).

 Net::SSLeay::PEM_get_string_X509($x509);
 # $x509 - value corresponding to openssl's X509 structure
 #
 # returns: string with $x509 in PEM format

=item * PEM_get_string_PrivateKey

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Converts public key $pk into PEM formatted string (optionally protected with password).

 my $rv = Net::SSLeay::PEM_get_string_PrivateKey($pk, $passwd, $enc_alg);
 # $pk - value corresponding to openssl's EVP_PKEY structure
 # $passwd - [optional] (string) password to use for key encryption
 # $enc_alg - [optional] algorithm to use for key encryption (default: DES_CBC) - value corresponding to openssl's EVP_CIPHER structure
 #
 # returns: PEM formatted string

Examples:

 $pem_privkey = Net::SSLeay::PEM_get_string_PrivateKey($pk);
 $pem_privkey = Net::SSLeay::PEM_get_string_PrivateKey($pk, "secret");
 $pem_privkey = Net::SSLeay::PEM_get_string_PrivateKey($pk, "secret", Net::SSLeay::EVP_get_cipherbyname("DES-EDE3-CBC"));

=item * PEM_get_string_X509_CRL

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Converts X509_CRL object $x509_crl into PEM formatted string.

 Net::SSLeay::PEM_get_string_X509_CRL($x509_crl);
 # $x509_crl - value corresponding to openssl's X509_CRL structure
 #
 # returns: no return value

=item * PEM_get_string_X509_REQ

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Converts X509_REQ object $x509_crl into PEM formatted string.

 Net::SSLeay::PEM_get_string_X509_REQ($x509_req);
 # $x509_req - value corresponding to openssl's X509_REQ structure
 #
 # returns: no return value

=back

=head3 Low level API: d2i_* (DER format) related functions

=over

=item * d2i_X509_bio

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Loads DER formatted X509 certificate via given BIO structure.

 my $rv = Net::SSLeay::d2i_X509_bio($bp);
 # $bp - value corresponding to openssl's BIO structure
 #
 # returns: value corresponding to openssl's X509 structure (0 on failure)

Example:

 my $bio = Net::SSLeay::BIO_new_file($filename, 'rb');
 my $x509 = Net::SSLeay::d2i_X509_bio($bio);
 Net::SSLeay::BIO_free($bio);

Check openssl doc L<http://www.openssl.org/docs/crypto/d2i_X509.html|http://www.openssl.org/docs/crypto/d2i_X509.html>

=item * d2i_X509_CRL_bio

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Loads DER formatted X509_CRL object via given BIO structure.

 my $rv = Net::SSLeay::d2i_X509_CRL_bio($bp);
 # $bp - value corresponding to openssl's BIO structure
 #
 # returns: value corresponding to openssl's X509_CRL structure (0 on failure)

Example:

 my $bio = Net::SSLeay::BIO_new_file($filename, 'rb');
 my $x509_crl = Net::SSLeay::d2i_X509_CRL_bio($bio);
 Net::SSLeay::BIO_free($bio);

=item * d2i_X509_REQ_bio

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Loads DER formatted X509_REQ object via given BIO structure.

 my $rv = Net::SSLeay::d2i_X509_REQ_bio($bp);
 # $bp - value corresponding to openssl's BIO structure
 #
 # returns: value corresponding to openssl's X509_REQ structure (0 on failure)

Example:

 my $bio = Net::SSLeay::BIO_new_file($filename, 'rb');
 my $x509_req = Net::SSLeay::d2i_X509_REQ_bio($bio);
 Net::SSLeay::BIO_free($bio);

=back

=head3 Low level API: PKCS12 related functions

=over

=item * P_PKCS12_load_file

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Loads X509 certificate + private key + certificates of CA chain (if present in PKCS12 file).

 my ($privkey, $cert, @cachain) = Net::SSLeay::P_PKCS12_load_file($filename, $load_chain, $password);
 # $filename - name of PKCS12 file
 # $load_chain - [optional] whether load (1) or not(0) CA chain (default: 0)
 # $password - [optional] password for private key
 #
 # returns: triplet ($privkey, $cert, @cachain)
 #          $privkey - value corresponding to openssl's EVP_PKEY structure
 #          $cert - value corresponding to openssl's X509 structure
 #          @cachain - array of values corresponding to openssl's X509 structure (empty if no CA chain in PKCS12)

B<IMPORTANT NOTE:> after you do the job you need to call X509_free() on $privkey + all members
of @cachain and EVP_PKEY_free() on $privkey.

Examples:

 my ($privkey, $cert) = Net::SSLeay::P_PKCS12_load_file($filename);
 #or
 my ($privkey, $cert) = Net::SSLeay::P_PKCS12_load_file($filename, 0, $password);
 #or
 my ($privkey, $cert, @cachain) = Net::SSLeay::P_PKCS12_load_file($filename, 1);
 #or
 my ($privkey, $cert, @cachain) = Net::SSLeay::P_PKCS12_load_file($filename, 1, $password);

 #BEWARE: THIS IS WRONG - MEMORY LEAKS! (you cannot free @cachain items)
 my ($privkey, $cert) = Net::SSLeay::P_PKCS12_load_file($filename, 1, $password);

B<NOTE> With some combinations of Windows, perl, compiler and compiler options, you
may see a runtime error "no OPENSSL_Applink", when calling
Net::SSLeay::P_PKCS12_load_file. See README.Win32 for more details.

=back

=head3 Low level API: SESSION_* related functions

=over

=item * d2i_SSL_SESSION

B<COMPATIBILITY:> does not work in Net-SSLeay-1.85 and before

Transforms the binary ASN1 representation string of an SSL/TLS session into an
SSL_SESSION object.

 my $ses = Net::SSLeay::d2i_SSL_SESSION($data);
 # $data - the session as ASN1 representation string
 #
 # returns: $ses - the new SSL_SESSION

Check openssl doc L<https://www.openssl.org/docs/ssl/i2d_SSL_SESSION.html|https://www.openssl.org/docs/ssl/i2d_SSL_SESSION.html>

=item * i2d_SSL_SESSION

B<COMPATIBILITY:> does not work in Net-SSLeay-1.85 and before

Transforms the SSL_SESSION object in into the ASN1 representation and returns
it as string.

 my $data = Net::SSLeay::i2d_SSL_SESSION($ses);
 # $ses - value corresponding to openssl's SSL_SESSION structure
 #
 # returns: $data - session as string

Check openssl doc L<https://www.openssl.org/docs/ssl/d2i_SSL_SESSION.html|https://www.openssl.org/docs/ssl/d2i_SSL_SESSION.html>

=item * SESSION_new

Creates a new SSL_SESSION structure.

 my $rv = Net::SSLeay::SESSION_new();
 #
 # returns: value corresponding to openssl's SSL_SESSION structure (0 on failure)

=item * SESSION_free

Free an allocated SSL_SESSION structure.

 Net::SSLeay::SESSION_free($ses);
 # $ses - value corresponding to openssl's SSL_SESSION structure
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_SESSION_free.html|http://www.openssl.org/docs/ssl/SSL_SESSION_free.html>

=item * SESSION_up_ref

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.0 or LibreSSL 2.7.0

Increases the reference counter on a SSL_SESSION structure.

 Net::SSLeay::SESSION_up_ref($ses);
 # $ses - value corresponding to openssl's SSL_SESSION structure
 #
 # returns: 1 on success else 0

Check openssl doc
L<https://www.openssl.org/docs/ssl/SSL_SESSION_up_ref.html|https://www.openssl.org/docs/ssl/SSL_SESSION_up_ref.html>

=item * SESSION_dup

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.1, not in LibreSSL

Duplicates a SSL_SESSION structure.

 Net::SSLeay::SESSION_dup($ses);
 # $ses - value corresponding to openssl's SSL_SESSION structure
 #
 # returns: the duplicated session

Check openssl doc
L<https://www.openssl.org/docs/ssl/SSL_SESSION_dup.html|https://www.openssl.org/docs/ssl/SSL_SESSION_dup.html>

=item * SESSION_is_resumable

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.1, not in LibreSSL

Determine whether an SSL_SESSION object can be used for resumption.

 Net::SSLeay::SESSION_is_resumable($ses);
 # $ses - value corresponding to openssl's SSL_SESSION structure
 #
 # returns: (integer) 1 if it can or 0 if not

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_SESSION_is_resumable.html|https://www.openssl.org/docs/manmaster/man3/SSL_SESSION_is_resumable.html>

=item * SESSION_cmp

Compare two SSL_SESSION structures.

 my $rv = Net::SSLeay::SESSION_cmp($sesa, $sesb);
 # $sesa - value corresponding to openssl's SSL_SESSION structure
 # $sesb - value corresponding to openssl's SSL_SESSION structure
 #
 # returns: 0 if the two structures are the same

B<NOTE:> Not available in openssl 1.0 or later

=item * SESSION_get_app_data

Can be used to get application defined value/data.

 my $rv = Net::SSLeay::SESSION_get_app_data($ses);
 # $ses - value corresponding to openssl's SSL_SESSION structure
 #
 # returns: string/buffer/pointer ???

=item * SESSION_set_app_data

Can be used to set some application defined value/data.

 my $rv = Net::SSLeay::SESSION_set_app_data($s, $a);
 # $s - value corresponding to openssl's SSL_SESSION structure
 # $a - (string/buffer/pointer ???) data
 #
 # returns: ???

=item * SESSION_get_ex_data

Is used to retrieve the information for $idx from session $ses.

 my $rv = Net::SSLeay::SESSION_get_ex_data($ses, $idx);
 # $ses - value corresponding to openssl's SSL_SESSION structure
 # $idx - (integer) index for application specific data
 #
 # returns: pointer to ???

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_SESSION_get_ex_new_index.html|http://www.openssl.org/docs/ssl/SSL_SESSION_get_ex_new_index.html>

=item * SESSION_set_ex_data

Is used to store application data at arg for idx into the session object.

 my $rv = Net::SSLeay::SESSION_set_ex_data($ss, $idx, $data);
 # $ss - value corresponding to openssl's SSL_SESSION structure
 # $idx - (integer) ???
 # $data - (pointer) ???
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_SESSION_get_ex_new_index.html|http://www.openssl.org/docs/ssl/SSL_SESSION_get_ex_new_index.html>

=item * SESSION_get_ex_new_index

Is used to register a new index for application specific data.

 my $rv = Net::SSLeay::SESSION_get_ex_new_index($argl, $argp, $new_func, $dup_func, $free_func);
 # $argl - (long) ???
 # $argp - (pointer) ???
 # $new_func - function pointer ??? (CRYPTO_EX_new *)
 # $dup_func - function pointer ??? (CRYPTO_EX_dup *)
 # $free_func - function pointer ??? (CRYPTO_EX_free *)
 #
 # returns: (integer) ???

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_SESSION_get_ex_new_index.html|http://www.openssl.org/docs/ssl/SSL_SESSION_get_ex_new_index.html>

=item * SESSION_get_master_key

B<NOTE:> Does not exactly correspond to any low level API function

Returns 'master_key' value from SSL_SESSION structure $s

 Net::SSLeay::SESSION_get_master_key($s);
 # $s - value corresponding to openssl's SSL_SESSION structure
 #
 # returns: master key (binary data)

=item * SESSION_set_master_key

Sets 'master_key' value for SSL_SESSION structure $s

 Net::SSLeay::SESSION_set_master_key($s, $key);
 # $s - value corresponding to openssl's SSL_SESSION structure
 # $key - master key (binary data)
 #
 # returns: no return value

Not available with OpenSSL 1.1 and later.
Code that previously used
       SESSION_set_master_key must now set $secret in the session_secret
       callback set with SSL_set_session_secret_cb.

=item * SESSION_get_time

Returns the time at which the session s was established.
The time is given in seconds since 1.1.1970.

 my $rv = Net::SSLeay::SESSION_get_time($s);
 # $s - value corresponding to openssl's SSL_SESSION structure
 #
 # returns: timestamp (seconds since 1.1.1970)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_SESSION_get_time.html|http://www.openssl.org/docs/ssl/SSL_SESSION_get_time.html>

=item * get_time

Technically the same functionality as L</SESSION_get_time>.

 my $rv = Net::SSLeay::get_time($s);

=item * SESSION_get_timeout

Returns the timeout value set for session $s in seconds.

 my $rv = Net::SSLeay::SESSION_get_timeout($s);
 # $s - value corresponding to openssl's SSL_SESSION structure
 #
 # returns: timeout (in seconds)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_SESSION_get_time.html|http://www.openssl.org/docs/ssl/SSL_SESSION_get_time.html>

=item * get_timeout

Technically the same functionality as L</SESSION_get_timeout>.

 my $rv = Net::SSLeay::get_timeout($s);

=item * SESSION_print

B<NOTE:> Does not exactly correspond to any low level API function

Prints session details (e.g. protocol version, cipher, session-id ...) to BIO.

 my $rv = Net::SSLeay::SESSION_print($fp, $ses);
 # $fp - value corresponding to openssl's BIO structure
 # $ses - value corresponding to openssl's SSL_SESSION structure
 #
 # returns: 1 on success, 0 on failure

You have to use necessary BIO functions like this:

 # let us have $ssl corresponding to openssl's SSL structure
 my $ses = Net::SSLeay::get_session($ssl);
 my $bio = Net::SSLeay::BIO_new(&Net::SSLeay::BIO_s_mem);
 Net::SSLeay::SESSION_print($bio, $ses);
 print Net::SSLeay::BIO_read($bio);

=item * SESSION_print_fp

Prints session details (e.g. protocol version, cipher, session-id ...) to file handle.

 my $rv = Net::SSLeay::SESSION_print_fp($fp, $ses);
 # $fp - perl file handle
 # $ses - value corresponding to openssl's SSL_SESSION structure
 #
 # returns: 1 on success, 0 on failure

Example:

 # let us have $ssl corresponding to openssl's SSL structure
 my $ses = Net::SSLeay::get_session($ssl);
 open my $fh, ">", "output.txt";
 Net::SSLeay::SESSION_print_fp($fh,$ses);

=item * SESSION_set_time

Replaces the creation time of the session s with the chosen value $t (seconds since 1.1.1970).

 my $rv = Net::SSLeay::SESSION_set_time($ses, $t);
 # $ses - value corresponding to openssl's SSL_SESSION structure
 # $t - time value
 #
 # returns: 1 on success

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_SESSION_get_time.html|http://www.openssl.org/docs/ssl/SSL_SESSION_get_time.html>

=item * set_time

Technically the same functionality as L</SESSION_set_time>.

 my $rv = Net::SSLeay::set_time($ses, $t);

=item * SESSION_set_timeout

Sets the timeout value for session s in seconds to $t.

 my $rv = Net::SSLeay::SESSION_set_timeout($s, $t);
 # $s - value corresponding to openssl's SSL_SESSION structure
 # $t - timeout (in seconds)
 #
 # returns: 1 on success

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_SESSION_get_time.html|http://www.openssl.org/docs/ssl/SSL_SESSION_get_time.html>

=item * set_timeout

Technically the same functionality as L</SESSION_set_timeout>.

 my $rv = Net::SSLeay::set_timeout($ses, $t);

=back

=head3 Low level API: SSL_CTX_* related functions

B<NOTE:> Please note that the function described in this chapter have "SSL_" part stripped from their original openssl names.

=over

=item * CTX_add_client_CA

Adds the CA name extracted from $cacert to the list of CAs sent to the client when requesting a client certificate for $ctx.

 my $rv = Net::SSLeay::CTX_add_client_CA($ctx, $cacert);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $cacert - value corresponding to openssl's X509 structure
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_client_CA_list.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_client_CA_list.html>

=item * CTX_add_extra_chain_cert

Adds the certificate $x509 to the certificate chain presented together with the certificate. Several certificates can be added one after the other.

 my $rv = Net::SSLeay::CTX_add_extra_chain_cert($ctx, $x509);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $x509 - value corresponding to openssl's X509 structure
 #
 # returns: 1 on success, check out the error stack to find out the reason for failure otherwise

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_add_extra_chain_cert.html|http://www.openssl.org/docs/ssl/SSL_CTX_add_extra_chain_cert.html>

=item * CTX_add_session

Adds the session $ses to the context $ctx.

 my $rv = Net::SSLeay::CTX_add_session($ctx, $ses);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $ses - value corresponding to openssl's SSL_SESSION structure
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_add_session.html|http://www.openssl.org/docs/ssl/SSL_CTX_add_session.html>

=item * CTX_callback_ctrl

??? (more info needed)

 my $rv = Net::SSLeay::CTX_callback_ctrl($ctx, $cmd, $fp);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $cmd - (integer) command id
 # $fp - (function pointer) ???
 #
 # returns: ???

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_ctrl.html|http://www.openssl.org/docs/ssl/SSL_CTX_ctrl.html>

=item * CTX_check_private_key

Checks the consistency of a private key with the corresponding certificate loaded into $ctx.

 my $rv = Net::SSLeay::CTX_check_private_key($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: 1 on success, otherwise check out the error stack to find out the reason

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html|http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

=item * CTX_ctrl

Internal handling function for SSL_CTX objects.

B<BEWARE:> openssl doc says: This function should never be called directly!

 my $rv = Net::SSLeay::CTX_ctrl($ctx, $cmd, $larg, $parg);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $cmd - (integer) command id
 # $larg - (integer) long ???
 # $parg - (string/pointer) ???
 #
 # returns: (long) result of given command ???

 #valid $cmd values
  1 - SSL_CTRL_NEED_TMP_RSA
  2 - SSL_CTRL_SET_TMP_RSA
  3 - SSL_CTRL_SET_TMP_DH
  4 - SSL_CTRL_SET_TMP_ECDH
  5 - SSL_CTRL_SET_TMP_RSA_CB
  6 - SSL_CTRL_SET_TMP_DH_CB
  7 - SSL_CTRL_SET_TMP_ECDH_CB
  8 - SSL_CTRL_GET_SESSION_REUSED
  9 - SSL_CTRL_GET_CLIENT_CERT_REQUEST
 10 - SSL_CTRL_GET_NUM_RENEGOTIATIONS
 11 - SSL_CTRL_CLEAR_NUM_RENEGOTIATIONS
 12 - SSL_CTRL_GET_TOTAL_RENEGOTIATIONS
 13 - SSL_CTRL_GET_FLAGS
 14 - SSL_CTRL_EXTRA_CHAIN_CERT
 15 - SSL_CTRL_SET_MSG_CALLBACK
 16 - SSL_CTRL_SET_MSG_CALLBACK_ARG
 17 - SSL_CTRL_SET_MTU
 20 - SSL_CTRL_SESS_NUMBER
 21 - SSL_CTRL_SESS_CONNECT
 22 - SSL_CTRL_SESS_CONNECT_GOOD
 23 - SSL_CTRL_SESS_CONNECT_RENEGOTIATE
 24 - SSL_CTRL_SESS_ACCEPT
 25 - SSL_CTRL_SESS_ACCEPT_GOOD
 26 - SSL_CTRL_SESS_ACCEPT_RENEGOTIATE
 27 - SSL_CTRL_SESS_HIT
 28 - SSL_CTRL_SESS_CB_HIT
 29 - SSL_CTRL_SESS_MISSES
 30 - SSL_CTRL_SESS_TIMEOUTS
 31 - SSL_CTRL_SESS_CACHE_FULL
 32 - SSL_CTRL_OPTIONS
 33 - SSL_CTRL_MODE
 40 - SSL_CTRL_GET_READ_AHEAD
 41 - SSL_CTRL_SET_READ_AHEAD
 42 - SSL_CTRL_SET_SESS_CACHE_SIZE
 43 - SSL_CTRL_GET_SESS_CACHE_SIZE
 44 - SSL_CTRL_SET_SESS_CACHE_MODE
 45 - SSL_CTRL_GET_SESS_CACHE_MODE
 50 - SSL_CTRL_GET_MAX_CERT_LIST
 51 - SSL_CTRL_SET_MAX_CERT_LIST
 52 - SSL_CTRL_SET_MAX_SEND_FRAGMENT
 53 - SSL_CTRL_SET_TLSEXT_SERVERNAME_CB
 54 - SSL_CTRL_SET_TLSEXT_SERVERNAME_ARG
 55 - SSL_CTRL_SET_TLSEXT_HOSTNAME
 56 - SSL_CTRL_SET_TLSEXT_DEBUG_CB
 57 - SSL_CTRL_SET_TLSEXT_DEBUG_ARG
 58 - SSL_CTRL_GET_TLSEXT_TICKET_KEYS
 59 - SSL_CTRL_SET_TLSEXT_TICKET_KEYS
 60 - SSL_CTRL_SET_TLSEXT_OPAQUE_PRF_INPUT
 61 - SSL_CTRL_SET_TLSEXT_OPAQUE_PRF_INPUT_CB
 62 - SSL_CTRL_SET_TLSEXT_OPAQUE_PRF_INPUT_CB_ARG
 63 - SSL_CTRL_SET_TLSEXT_STATUS_REQ_CB
 64 - SSL_CTRL_SET_TLSEXT_STATUS_REQ_CB_ARG
 65 - SSL_CTRL_SET_TLSEXT_STATUS_REQ_TYPE
 66 - SSL_CTRL_GET_TLSEXT_STATUS_REQ_EXTS
 67 - SSL_CTRL_SET_TLSEXT_STATUS_REQ_EXTS
 68 - SSL_CTRL_GET_TLSEXT_STATUS_REQ_IDS
 69 - SSL_CTRL_SET_TLSEXT_STATUS_REQ_IDS
 70 - SSL_CTRL_GET_TLSEXT_STATUS_REQ_OCSP_RESP
 71 - SSL_CTRL_SET_TLSEXT_STATUS_REQ_OCSP_RESP
 72 - SSL_CTRL_SET_TLSEXT_TICKET_KEY_CB
 73 - DTLS_CTRL_GET_TIMEOUT
 74 - DTLS_CTRL_HANDLE_TIMEOUT
 75 - DTLS_CTRL_LISTEN
 76 - SSL_CTRL_GET_RI_SUPPORT
 77 - SSL_CTRL_CLEAR_OPTIONS
 78 - SSL_CTRL_CLEAR_MODE

 82 - SSL_CTRL_GET_EXTRA_CHAIN_CERTS
 83 - SSL_CTRL_CLEAR_EXTRA_CHAIN_CERTS

 88 - SSL_CTRL_CHAIN
 89 - SSL_CTRL_CHAIN_CERT

 90 - SSL_CTRL_GET_CURVES
 91 - SSL_CTRL_SET_CURVES
 92 - SSL_CTRL_SET_CURVES_LIST
 93 - SSL_CTRL_GET_SHARED_CURVE 
 94 - SSL_CTRL_SET_ECDH_AUTO
 97 - SSL_CTRL_SET_SIGALGS
 98 - SSL_CTRL_SET_SIGALGS_LIST
 99 - SSL_CTRL_CERT_FLAGS
 100 - SSL_CTRL_CLEAR_CERT_FLAGS
 101 - SSL_CTRL_SET_CLIENT_SIGALGS
 102 - SSL_CTRL_SET_CLIENT_SIGALGS_LIST
 103 - SSL_CTRL_GET_CLIENT_CERT_TYPES
 104 - SSL_CTRL_SET_CLIENT_CERT_TYPES
 105 - SSL_CTRL_BUILD_CERT_CHAIN
 106 - SSL_CTRL_SET_VERIFY_CERT_STORE
 107 - SSL_CTRL_SET_CHAIN_CERT_STORE
 108 - SSL_CTRL_GET_PEER_SIGNATURE_NID
 109 - SSL_CTRL_GET_SERVER_TMP_KEY
 110 - SSL_CTRL_GET_RAW_CIPHERLIST
 111 - SSL_CTRL_GET_EC_POINT_FORMATS
 112 - SSL_CTRL_GET_TLSA_RECORD
 113 - SSL_CTRL_SET_TLSA_RECORD
 114 - SSL_CTRL_PULL_TLSA_RECORD 

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_ctrl.html|http://www.openssl.org/docs/ssl/SSL_CTX_ctrl.html>

=item * CTX_flush_sessions

Causes a run through the session cache of $ctx to remove sessions expired at time $tm.

 Net::SSLeay::CTX_flush_sessions($ctx, $tm);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $tm - specifies the time which should be used for the expiration test (seconds since 1.1.1970)
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_flush_sessions.html|http://www.openssl.org/docs/ssl/SSL_CTX_flush_sessions.html>

=item * CTX_free

Free an allocated SSL_CTX object.

 Net::SSLeay::CTX_free($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_free.html|http://www.openssl.org/docs/ssl/SSL_CTX_free.html>

=item * CTX_get_app_data

Can be used to get application defined value/data.

 my $rv = Net::SSLeay::CTX_get_app_data($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: string/buffer/pointer ???

=item * CTX_set_app_data

Can be used to set some application defined value/data.

 my $rv = Net::SSLeay::CTX_set_app_data($ctx, $arg);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $arg - (string/buffer/pointer ???) data
 #
 # returns: ???

=item * CTX_get0_param

B<COMPATIBILITY:> not available in Net-SSLeay-1.82 and before; requires at least OpenSSL 1.0.2

Returns the current verification parameters.

 my $vpm = Net::SSLeay::CTX_get0_param($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: value corresponding to openssl's X509_VERIFY_PARAM structure

Check openssl doc L<https://www.openssl.org/docs/ssl/SSL_CTX_get0_param.html|https://www.openssl.org/docs/ssl/SSL_CTX_get0_param.html>

=item * CTX_get_cert_store

Returns the current certificate verification storage.

 my $rv = Net::SSLeay::CTX_get_cert_store($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: value corresponding to openssl's X509_STORE structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_cert_store.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_cert_store.html>

=item * CTX_get_client_CA_list

Returns the list of client CAs explicitly set for $ctx using L</CTX_set_client_CA_list>.

 my $rv = Net::SSLeay::CTX_get_client_CA_list($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: value corresponding to openssl's X509_NAME_STACK structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_get_client_CA_list.html|http://www.openssl.org/docs/ssl/SSL_get_client_CA_list.html>

=item * CTX_get_ex_data

Is used to retrieve the information for index $idx from $ctx.

 my $rv = Net::SSLeay::CTX_get_ex_data($ssl, $idx);
 # $ssl - value corresponding to openssl's SSL_CTX structure
 # $idx - (integer) index for application specific data
 #
 # returns: pointer to ???

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_get_ex_new_index.html|http://www.openssl.org/docs/ssl/SSL_CTX_get_ex_new_index.html>

=item * CTX_get_ex_new_index

Is used to register a new index for application specific data.

 my $rv = Net::SSLeay::CTX_get_ex_new_index($argl, $argp, $new_func, $dup_func, $free_func);
 # $argl - (long) ???
 # $argp - (pointer) ???
 # $new_func - function pointer ??? (CRYPTO_EX_new *)
 # $dup_func - function pointer ??? (CRYPTO_EX_dup *)
 # $free_func - function pointer ??? (CRYPTO_EX_free *)
 #
 # returns: (integer) ???

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_get_ex_new_index.html|http://www.openssl.org/docs/ssl/SSL_CTX_get_ex_new_index.html>

=item * CTX_get_mode

Returns the mode set for ctx.

 my $rv = Net::SSLeay::CTX_get_mode($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: mode (bitmask)

 #to decode the return value (bitmask) use:
 0x00000001 corresponds to SSL_MODE_ENABLE_PARTIAL_WRITE
 0x00000002 corresponds to SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER
 0x00000004 corresponds to SSL_MODE_AUTO_RETRY
 0x00000008 corresponds to SSL_MODE_NO_AUTO_CHAIN
 0x00000010 corresponds to SSL_MODE_RELEASE_BUFFERS
 (note: some of the bits might not be supported by older openssl versions)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_mode.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_mode.html>

=item * CTX_set_mode

Adds the mode set via bitmask in $mode to $ctx. Options already set before are not cleared.

 my $rv = Net::SSLeay::CTX_set_mode($ctx, $mode);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $mode - mode bitmask
 #
 # returns: the new mode bitmask after adding $mode

For bitmask details see L</CTX_get_mode> (above).

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_mode.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_mode.html>

=item * CTX_get_options

Returns the options (bitmask) set for $ctx.

 my $rv = Net::SSLeay::CTX_get_options($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: options (bitmask)

B<BEWARE:> The available constants and their values in bitmask depend
on the TLS library. For example, SSL_OP_NO_TLSv1_3 became available
much later than SSL_OP_NO_COMPRESS which is already deprecated by some
libraries. Also, some previously used option values have been recycled
and are now used for newer options. See the list of constants in this
document for options Net::SSLeay currently supports.

You are strongly encouraged to B<check your TLS library> if you need
to use numeric values directly. The following is a sample of historic
values. It may not be correct anymore.

 #to decode the return value (bitmask) use:
 0x00000004 corresponds to SSL_OP_LEGACY_SERVER_CONNECT
 0x00000800 corresponds to SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
 0x00004000 corresponds to SSL_OP_NO_TICKET
 0x00010000 corresponds to SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
 0x00400000 corresponds to SSL_OP_CIPHER_SERVER_PREFERENCE
 0x04000000 corresponds to SSL_OP_NO_TLSv1

Check openssl doc L<https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_options.html|https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_options.html>

=item * CTX_set_options

Adds the options set via bitmask in $options to ctx. Options already set before are not cleared.

 Net::SSLeay::CTX_set_options($ctx, $options);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $options - options bitmask
 #
 # returns: the new options bitmask after adding $options

For bitmask details see L</CTX_get_options> (above).

Check openssl doc L<https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_options.html|https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_options.html>

=item * CTX_get_quiet_shutdown

Returns the 'quiet shutdown' setting of $ctx.

 my $rv = Net::SSLeay::CTX_get_quiet_shutdown($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: (integer) the current setting

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_quiet_shutdown.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_quiet_shutdown.html>

=item * CTX_get_read_ahead

 my $rv = Net::SSLeay::CTX_get_read_ahead($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: (integer) read_ahead value

=item * CTX_get_session_cache_mode

Returns the currently used cache mode (bitmask).

 my $rv = Net::SSLeay::CTX_get_session_cache_mode($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: mode (bitmask)

B<BEWARE:> SESS_CACHE_OFF and other constants are not available in
Net-SSLeay-1.82 and before.  If the constants are not available, the
following values have historically been correct. You are strongly
encouraged to B<check your TLS library> for the current values.

 #to decode the return value (bitmask) use:
 0x0000 corresponds to SSL_SESS_CACHE_OFF
 0x0001 corresponds to SSL_SESS_CACHE_CLIENT
 0x0002 corresponds to SSL_SESS_CACHE_SERVER
 0x0080 corresponds to SSL_SESS_CACHE_NO_AUTO_CLEAR
 0x0100 corresponds to SSL_SESS_CACHE_NO_INTERNAL_LOOKUP
 0x0200 corresponds to SSL_SESS_CACHE_NO_INTERNAL_STORE
 (note: some of the bits might not be supported by older openssl versions)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_session_cache_mode.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_session_cache_mode.html>

=item * CTX_set_session_cache_mode

Enables/disables session caching by setting the operational mode for $ctx to $mode.

 my $rv = Net::SSLeay::CTX_set_session_cache_mode($ctx, $mode);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $mode - mode (bitmask)
 #
 # returns: previously set cache mode

For bitmask details see L</CTX_get_session_cache_mode> (above).

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_session_cache_mode.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_session_cache_mode.html>

=item * CTX_get_timeout

Returns the currently set timeout value for $ctx.

 my $rv = Net::SSLeay::CTX_get_timeout($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: timeout in seconds

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_timeout.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_timeout.html>

=item * CTX_get_verify_depth

Returns the verification depth limit currently set in $ctx. If no limit has been explicitly set, -1 is returned and the default value will be used.",

 my $rv = Net::SSLeay::CTX_get_verify_depth($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: depth limit currently set in $ctx, -1 if no limit has been explicitly set

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_get_verify_mode.html|http://www.openssl.org/docs/ssl/SSL_CTX_get_verify_mode.html>

=item * CTX_get_verify_mode

Returns the verification mode (bitmask) currently set in $ctx.

 my $rv = Net::SSLeay::CTX_get_verify_mode($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: mode (bitmask)

For bitmask details see L</"CTX_set_verify">.

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get_verify_mode.html|https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get_verify_mode.html>

=item * CTX_set_verify

Sets the verification flags for $ctx to be $mode and specifies the verify_callback function to be used.

 Net::SSLeay::CTX_set_verify($ctx, $mode, $callback);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $mode - mode (bitmask), see OpenSSL manual
 # $callback - [optional] reference to perl callback function
 #
 # returns: no return value

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_verify.html|https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_verify.html>

=item * CTX_set_post_handshake_auth

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.1, not in LibreSSL

Enable the Post-Handshake Authentication extension to be added to the ClientHello such that post-handshake authentication can be requested by the server.

 Net::SSLeay::CTX_set_posthandshake_auth($ctx, $val);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $val - 0 then the extension is not sent, otherwise it is
 #
 # returns: no return value

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_post_handshake_auth|https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_post_handshake_auth.html>

=item * CTX_load_verify_locations

Specifies the locations for $ctx, at which CA certificates for verification purposes are located. The certificates available via $CAfile and $CApath are trusted.

 my $rv = Net::SSLeay::CTX_load_verify_locations($ctx, $CAfile, $CApath);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $CAfile - (string) file of CA certificates in PEM format, the file can contain several CA certificates (or '')
 # $CApath - (string) directory containing CA certificates in PEM format (or '')
 #
 # returns: 1 on success, 0 on failure (check the error stack to find out the reason)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_load_verify_locations.html|http://www.openssl.org/docs/ssl/SSL_CTX_load_verify_locations.html>

=item * CTX_need_tmp_RSA

Return the result of C<SSL_CTX_ctrl(ctx,SSL_CTRL_NEED_TMP_RSA,0,NULL)>

 my $rv = Net::SSLeay::CTX_need_tmp_RSA($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: result of SSL_CTRL_NEED_TMP_RSA command

Not available with OpenSSL 1.1 and later.

=item * CTX_new

The same as L</CTX_v23_new>

 my $rv = Net::SSLeay::CTX_new();
 #
 # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_new.html|http://www.openssl.org/docs/ssl/SSL_CTX_new.html>

Not available with OpenSSL 1.1 and later.

=item * CTX_v2_new

Creates a new SSL_CTX object - based on SSLv2_method() - as framework to establish TLS/SSL enabled connections.

 my $rv = Net::SSLeay::CTX_v2_new();
 #
 # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

=item * CTX_v23_new

Creates a new SSL_CTX object - based on SSLv23_method() - as framework to establish TLS/SSL enabled connections.

 my $rv = Net::SSLeay::CTX_v23_new();
 #
 # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

=item * CTX_v3_new

Creates a new SSL_CTX object - based on SSLv3_method() - as framework to establish TLS/SSL enabled connections.

 my $rv = Net::SSLeay::CTX_v3_new();
 #
 # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

=item * CTX_tlsv1_new

Creates a new SSL_CTX object - based on TLSv1_method() - as framework to establish TLS/SSL enabled connections.

 my $rv = Net::SSLeay::CTX_tlsv1_new();
 #
 # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

=item * CTX_tlsv1_1_new

Creates a new SSL_CTX object - based on TLSv1_1_method() - as framework to establish TLS/SSL 
enabled connections. Only available where supported by the underlying openssl.

 my $rv = Net::SSLeay::CTX_tlsv1_1_new();
 #
 # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

=item * CTX_tlsv1_2_new

Creates a new SSL_CTX object - based on TLSv1_2_method() - as framework to establish TLS/SSL 
enabled connections. Only available where supported by the underlying openssl.

 my $rv = Net::SSLeay::CTX_tlsv1_2_new();
 #
 # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

=item * CTX_new_with_method

Creates a new SSL_CTX object based on $meth method

 my $rv = Net::SSLeay::CTX_new_with_method($meth);
 # $meth - value corresponding to openssl's SSL_METHOD structure
 #
 # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

 #example
 my $ctx = Net::SSLeay::CTX_new_with_method(&Net::SSLeay::TLSv1_method);

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_new.html|http://www.openssl.org/docs/ssl/SSL_CTX_new.html>

=item * CTX_set_min_proto_version, CTX_set_max_proto_version, set_min_proto_version and set_max_proto_version,

B<COMPATIBILITY:> not available in Net-SSLeay-1.82 and before; requires at least OpenSSL 1.1.0 or LibreSSL 2.6.0

Set the minimum and maximum supported protocol for $ctx or $ssl.

 my $rv = Net::SSLeay::CTX_set_min_proto_version($ctx, $version)
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $version - (integer) constat version value or 0 for automatic lowest or highest value
 #
 # returns: 1 on success, 0 on failure

 #example: allow only TLS 1.2 for a SSL_CTX
 my $rv_min = Net::SSLeay::CTX_set_min_proto_version($ctx, Net::SSLeay::TLS1_2_VERSION());
 my $rv_max = Net::SSLeay::CTX_set_max_proto_version($ctx, Net::SSLeay::TLS1_2_VERSION());

 #example: allow only TLS 1.1 for a SSL
 my $rv_min = Net::SSLeay::set_min_proto_version($ssl, Net::SSLeay::TLS1_1_VERSION());
 my $rv_max = Net::SSLeay::set_max_proto_version($ssl, Net::SSLeay::TLS1_1_VERSION());

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_min_proto_version.html|https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_min_proto_version.html>

=item * CTX_get_min_proto_version, CTX_get_max_proto_version, get_min_proto_version and get_max_proto_version,

B<COMPATIBILITY:> not available in Net-SSLeay-1.82 and before; requires at least OpenSSL 1.1.0g

Get the minimum and maximum supported protocol for $ctx or $ssl.

 my $version = Net::SSLeay::CTX_get_min_proto_version($ctx)
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: 0 automatic lowest or highest value, configured value otherwise

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_min_proto_version.html|https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_min_proto_version.html>

=item * CTX_remove_session

Removes the session $ses from the context $ctx.

 my $rv = Net::SSLeay::CTX_remove_session($ctx, $ses);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $ses - value corresponding to openssl's SSL_SESSION structure
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_add_session.html|http://www.openssl.org/docs/ssl/SSL_CTX_add_session.html>

=item * CTX_sess_accept

 my $rv = Net::SSLeay::CTX_sess_accept($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: number of started SSL/TLS handshakes in server mode

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html|http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

=item * CTX_sess_accept_good

 my $rv = Net::SSLeay::CTX_sess_accept_good($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: number of successfully established SSL/TLS sessions in server mode

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html|http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

=item * CTX_sess_accept_renegotiate

 my $rv = Net::SSLeay::CTX_sess_accept_renegotiate($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: number of start renegotiations in server mode

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html|http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

=item * CTX_sess_cache_full

 my $rv = Net::SSLeay::CTX_sess_cache_full($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: number of sessions that were removed because the maximum session cache size was exceeded

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html|http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

=item * CTX_sess_cb_hits

 my $rv = Net::SSLeay::CTX_sess_cb_hits($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: number of successfully retrieved sessions from the external session cache in server mode

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html|http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

=item * CTX_sess_connect

 my $rv = Net::SSLeay::CTX_sess_connect($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: number of started SSL/TLS handshakes in client mode

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html|http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

=item * CTX_sess_connect_good

 my $rv = Net::SSLeay::CTX_sess_connect_good($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: number of successfully established SSL/TLS sessions in client mode

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html|http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

=item * CTX_sess_connect_renegotiate

 my $rv = Net::SSLeay::CTX_sess_connect_renegotiate($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: number of start renegotiations in client mode

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html|http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

=item * CTX_sess_get_cache_size

Returns the currently valid session cache size.

 my $rv = Net::SSLeay::CTX_sess_get_cache_size($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: current size

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_sess_set_cache_size.html|http://www.openssl.org/docs/ssl/SSL_CTX_sess_set_cache_size.html>

=item * CTX_sess_hits

 my $rv = Net::SSLeay::CTX_sess_hits($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: number of successfully reused sessions

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html|http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

=item * CTX_sess_misses

 my $rv = Net::SSLeay::CTX_sess_misses($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: number of sessions proposed by clients that were not found in the internal session cache in server mode

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html|http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

=item * CTX_sess_number

 my $rv = Net::SSLeay::CTX_sess_number($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: current number of sessions in the internal session cache

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html|http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

=item * CTX_sess_set_cache_size

Sets the size of the internal session cache of context $ctx to $size.

 Net::SSLeay::CTX_sess_set_cache_size($ctx, $size);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $size - cache size (0 = unlimited)
 #
 # returns: previously valid size

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_sess_set_cache_size.html|http://www.openssl.org/docs/ssl/SSL_CTX_sess_set_cache_size.html>

=item * CTX_sess_timeouts

Returns the number of sessions proposed by clients and either found in the internal or external session cache in
server mode, but that were invalid due to timeout. These sessions are not included in the SSL_CTX_sess_hits count.

 my $rv = Net::SSLeay::CTX_sess_timeouts($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: number of sessions

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html|http://www.openssl.org/docs/ssl/SSL_CTX_sess_number.html>

=item * CTX_sess_set_new_cb

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before

Sets the callback function, which is automatically called whenever a new session was negotiated.

 Net::SSLeay::CTX_sess_set_new_cb($ctx, $func);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $func - perl reference to callback function
 #
 # returns: no return value

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sess_set_new_cb.html|https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sess_set_new_cb.html>

=item * CTX_sess_set_remove_cb

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before

Sets the callback function, which is automatically called whenever a session is removed by the SSL engine.

 Net::SSLeay::CTX_sess_set_remove_cb($ctx, $func);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $func - perl reference to callback function
 #
 # returns: no return value

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sess_set_remove_cb.html|https://www.openssl.org/docs/manmaster/man3/SSL_CTX_sess_set_remove_cb.html>

=item * CTX_sessions

Returns a pointer to the lhash databases containing the internal session cache for ctx.

 my $rv = Net::SSLeay::CTX_sessions($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: value corresponding to openssl's LHASH structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_sessions.html|http://www.openssl.org/docs/ssl/SSL_CTX_sessions.html>

=item * CTX_set1_param

Applies X509 verification parameters $vpm on $ctx

 my $rv = Net::SSLeay::CTX_set1_param($ctx, $vpm);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $vpm - value corresponding to openssl's X509_VERIFY_PARAM structure
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<https://www.openssl.org/docs/ssl/SSL_CTX_get0_param.html|https://www.openssl.org/docs/ssl/SSL_CTX_get0_param.html>

=item * CTX_set_cert_store

Sets/replaces the certificate verification storage of $ctx to/with $store.

 Net::SSLeay::CTX_set_cert_store($ctx, $store);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $store - value corresponding to openssl's X509_STORE structure
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_cert_store.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_cert_store.html>

=item * CTX_set_cert_verify_callback

Sets the verification callback function for $ctx. SSL objects that are created from $ctx
inherit the setting valid at the time when C<Net::SSLeay::new($ctx)> is called.

 Net::SSLeay::CTX_set_cert_verify_callback($ctx, $func, $data);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $func - perl reference to callback function
 # $data - [optional] data that will be passed to callback function when invoked
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_cert_verify_callback.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_cert_verify_callback.html>

=item * CTX_set_cipher_list

Sets the list of available ciphers for $ctx using the control string $str.
The list of ciphers is inherited by all ssl objects created from $ctx.

 my $rv = Net::SSLeay::CTX_set_cipher_list($s, $str);
 # $s - value corresponding to openssl's SSL_CTX structure
 # $str - (string) cipher list e.g. '3DES:+RSA'
 #
 # returns: 1 if any cipher could be selected and 0 on complete failure

The format of $str is described in L<http://www.openssl.org/docs/apps/ciphers.html|http://www.openssl.org/docs/apps/ciphers.html>

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_cipher_list.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_cipher_list.html>

=item * CTX_set_ciphersuites

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.1, not in LibreSSL

Configure the available TLSv1.3 ciphersuites.

 my $rv = Net::SSLeay::CTX_set_ciphersuites($ctx, $str);
 # $ctx  - value corresponding to openssl's SSL_CTX structure
 # $str  - colon (":") separated list of TLSv1.3 ciphersuite names in order of preference
 #
 # returns: (integer) 1 if the requested ciphersuite list was configured, and 0 otherwise

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_ciphersuites.html|https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_ciphersuites.html>

=item * CTX_set_client_CA_list

Sets the list of CAs sent to the client when requesting a client certificate for $ctx.

 Net::SSLeay::CTX_set_client_CA_list($ctx, $list);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $list - value corresponding to openssl's X509_NAME_STACK structure
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_client_CA_list.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_client_CA_list.html>

=item * CTX_set_default_passwd_cb

Sets the default password callback called when loading/storing a PEM certificate with encryption.

 Net::SSLeay::CTX_set_default_passwd_cb($ctx, $func);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $func - perl reference to callback function
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_default_passwd_cb.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_default_passwd_cb.html>

=item * CTX_set_default_passwd_cb_userdata

Sets a pointer to userdata which will be provided to the password callback on invocation.

 Net::SSLeay::CTX_set_default_passwd_cb_userdata($ctx, $userdata);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $userdata - data that will be passed to callback function when invoked
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_default_passwd_cb.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_default_passwd_cb.html>

=item * CTX_set_default_verify_paths

??? (more info needed)

 my $rv = Net::SSLeay::CTX_set_default_verify_paths($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: 1 on success, 0 on failure

=item * CTX_set_ex_data

Is used to store application data at $data for $idx into the $ctx object.

 my $rv = Net::SSLeay::CTX_set_ex_data($ssl, $idx, $data);
 # $ssl - value corresponding to openssl's SSL_CTX structure
 # $idx - (integer) ???
 # $data - (pointer) ???
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_get_ex_new_index.html|http://www.openssl.org/docs/ssl/SSL_CTX_get_ex_new_index.html>

=item * CTX_set_purpose

 my $rv = Net::SSLeay::CTX_set_purpose($s, $purpose);
 # $s - value corresponding to openssl's SSL_CTX structure
 # $purpose - (integer) purpose identifier
 #
 # returns: 1 on success, 0 on failure

 #avainable purpose identifier
 1 - X509_PURPOSE_SSL_CLIENT
 2 - X509_PURPOSE_SSL_SERVER
 3 - X509_PURPOSE_NS_SSL_SERVER
 4 - X509_PURPOSE_SMIME_SIGN
 5 - X509_PURPOSE_SMIME_ENCRYPT
 6 - X509_PURPOSE_CRL_SIGN
 7 - X509_PURPOSE_ANY
 8 - X509_PURPOSE_OCSP_HELPER
 9 - X509_PURPOSE_TIMESTAMP_SIGN

 #or use corresponding constants
 $purpose = &Net::SSLeay::X509_PURPOSE_SSL_CLIENT;
 ...
 $purpose = &Net::SSLeay::X509_PURPOSE_TIMESTAMP_SIGN;

=item * CTX_set_quiet_shutdown

Sets the 'quiet shutdown' flag for $ctx to be mode. SSL objects created from $ctx inherit the mode valid at the time C<Net::SSLeay::new($ctx)> is called.

 Net::SSLeay::CTX_set_quiet_shutdown($ctx, $mode);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $mode - 0 or 1
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_quiet_shutdown.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_quiet_shutdown.html>

=item * CTX_set_read_ahead

 my $rv = Net::SSLeay::CTX_set_read_ahead($ctx, $val);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $val - read_ahead value to be set
 #
 # returns: the original read_ahead value

=item * CTX_set_session_id_context

Sets the context $sid_ctx of length $sid_ctx_len within which a session can be reused for the $ctx object.

 my $rv = Net::SSLeay::CTX_set_session_id_context($ctx, $sid_ctx, $sid_ctx_len);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $sid_ctx - data buffer
 # $sid_ctx_len - length of data in $sid_ctx
 #
 # returns: 1 on success, 0 on failure (the error is logged to the error stack)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_session_id_context.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_session_id_context.html>

=item * CTX_set_ssl_version

Sets a new default TLS/SSL method for SSL objects newly created from this $ctx.
SSL objects already created with C<Net::SSLeay::new($ctx)> are not
affected, except when C<Net::SSLeay:clear($ssl)> is being called.

 my $rv = Net::SSLeay::CTX_set_ssl_version($ctx, $meth);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $meth - value corresponding to openssl's SSL_METHOD structure
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_ssl_version.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_ssl_version.html>

=item * CTX_set_timeout

Sets the timeout for newly created sessions for $ctx to $t. The timeout value $t must be given in seconds.

 my $rv = Net::SSLeay::CTX_set_timeout($ctx, $t);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $t - timeout in seconds
 #
 # returns: previously set timeout value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_timeout.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_timeout.html>

=item * CTX_set_tmp_dh

Sets DH parameters to be used to be $dh. The key is inherited by all ssl objects created from $ctx.

 my $rv = Net::SSLeay::CTX_set_tmp_dh($ctx, $dh);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $dh - value corresponding to openssl's DH structure
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_dh_callback.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_dh_callback.html>

=item * CTX_set_tmp_dh_callback

Sets the callback function for $ctx to be used when a DH parameters are required to $tmp_dh_callback.

 Net::SSLeay::CTX_set_tmp_dh_callback($ctx, $tmp_dh_callback);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # tmp_dh_callback - (function pointer) ???
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_dh_callback.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_dh_callback.html>

=item * CTX_set_tmp_rsa

Sets the temporary/ephemeral RSA key to be used to be $rsa.

 my $rv = Net::SSLeay::CTX_set_tmp_rsa($ctx, $rsa);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $rsa - value corresponding to openssl's RSA structure
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_rsa_callback.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_rsa_callback.html>

Not available with OpenSSL 1.1 and later.

=item * CTX_set_tmp_rsa_callback

Sets the callback function for ctx to be used when a temporary/ephemeral RSA key is required to $tmp_rsa_callback.

??? (does this function really work?)

 Net::SSLeay::CTX_set_tmp_rsa_callback($ctx, $tmp_rsa_callback);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $tmp_rsa_callback - (function pointer) ???
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_rsa_callback.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_rsa_callback.html>

Not available with OpenSSL 1.1 and later.

=item * CTX_set_trust

 my $rv = Net::SSLeay::CTX_set_trust($s, $trust);
 # $s - value corresponding to openssl's SSL_CTX structure
 # $trust - (integer) trust identifier
 #
 # returns: the original value

 #available trust identifiers
 1 - X509_TRUST_COMPAT
 2 - X509_TRUST_SSL_CLIENT
 3 - X509_TRUST_SSL_SERVER
 4 - X509_TRUST_EMAIL
 5 - X509_TRUST_OBJECT_SIGN
 6 - X509_TRUST_OCSP_SIGN
 7 - X509_TRUST_OCSP_REQUEST
 8 - X509_TRUST_TSA

 #or use corresponding constants
 $trust = &Net::SSLeay::X509_TRUST_COMPAT;
 ...
 $trust = &Net::SSLeay::X509_TRUST_TSA;

=item * CTX_set_verify_depth

Sets the maximum depth for the certificate chain verification that shall be allowed for ctx.

 Net::SSLeay::CTX_set_verify_depth($ctx, $depth);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $depth - max. depth
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_verify.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_verify.html>

=item * CTX_use_PKCS12_file

Adds the certificate and private key from PKCS12 file $p12filename to $ctx.

 my $rv = Net::SSLeay::CTX_use_PKCS12_file($ctx, $p12filename, $password);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $p12filename - (string) filename
 # $password - (string) password to decrypt private key
 #
 # returns: 1 on success, 0 on failure

=item * CTX_use_PrivateKey

Adds the private key $pkey to $ctx.

 my $rv = Net::SSLeay::CTX_use_PrivateKey($ctx, $pkey);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $pkey - value corresponding to openssl's EVP_PKEY structure
 #
 # returns: 1 on success, otherwise check out the error stack to find out the reason

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html|http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

=item * CTX_use_PrivateKey_file

Adds the first private key found in $file to $ctx.

 my $rv = Net::SSLeay::CTX_use_PrivateKey_file($ctx, $file, $type);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $file - (string) file name
 # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
 #
 # returns: 1 on success, otherwise check out the error stack to find out the reason

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html|http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

=item * CTX_use_RSAPrivateKey

Adds the RSA private key $rsa to $ctx.

 my $rv = Net::SSLeay::CTX_use_RSAPrivateKey($ctx, $rsa);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $rsa - value corresponding to openssl's RSA structure
 #
 # returns: 1 on success, otherwise check out the error stack to find out the reason

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html|http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

=item * CTX_use_RSAPrivateKey_file

Adds the first RSA private key found in $file to $ctx.

 my $rv = Net::SSLeay::CTX_use_RSAPrivateKey_file($ctx, $file, $type);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $file - (string) file name
 # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
 #
 # returns: 1 on success, otherwise check out the error stack to find out the reason

=item * CTX_use_certificate

Loads the certificate $x into $ctx

 my $rv = Net::SSLeay::CTX_use_certificate($ctx, $x);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $x - value corresponding to openssl's X509 structure
 #
 # returns: 1 on success, otherwise check out the error stack to find out the reason

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html|http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

=item * CTX_use_certificate_chain_file

Loads a certificate chain from $file into $ctx. The certificates must be in PEM format and must be sorted
starting with the subject's certificate (actual client or server certificate), followed by intermediate
CA certificates if applicable, and ending at the highest level (root) CA.

 my $rv = Net::SSLeay::CTX_use_certificate_chain_file($ctx, $file);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $file - (string) file name
 #
 # returns: 1 on success, otherwise check out the error stack to find out the reason

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html|http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

=item * CTX_use_certificate_file

Loads the first certificate stored in $file into $ctx.

 my $rv = Net::SSLeay::CTX_use_certificate_file($ctx, $file, $type);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $file - (string) file name
 # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
 #
 # returns: 1 on success, otherwise check out the error stack to find out the reason

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html|http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

=item * CTX_get_security_level

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.0, not in LibreSSL

Returns the security level associated with $ctx.

 my $level = Net::SSLeay::CTX_get_security_level($ctx);
 # $ctx   - value corresponding to openssl's SSL_CTX structure
 #
 # returns: (integer) current security level

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get_security_level.html|https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get_security_level.html>

=item * CTX_set_security_level

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.0, not in LibreSSL

Sets the security level associated with $ctx to $level.

 Net::SSLeay::CTX_set_security_level($ctx, $level);
 # $ssl   - value corresponding to openssl's SSL_CTX structure
 # $level - new security level
 #
 # returns: no return value

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_security_level.html|https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_security_level.html>

=item * CTX_set_num_tickets

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.1, not in LibreSSL

Set number of TLSv1.3 session tickets that will be sent to a client.

 my $rv = Net::SSLeay::CTX_set_num_tickets($ctx, $number_of_tickets);
 # $ctx  - value corresponding to openssl's SSL_CTX structure
 # $number_of_tickets - number of tickets to send
 #
 # returns: 1 on success, 0 on failure

Set to zero if you do not no want to support a session resumption.

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_num_tickets.html|https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_num_tickets.html>

=item * CTX_get_num_tickets

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.1, not in LibreSSL

Get number of TLSv1.3 session tickets that will be sent to a client.

 my $number_of_tickets = Net::SSLeay::CTX_get_num_tickets($ctx);
 # $ctx  - value corresponding to openssl's SSL_CTX structure
 #
 # returns: (integer) number of tickets to send

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get_num_tickets.html|https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get_num_tickets.html>

=back

=head3 Low level API: SSL_* related functions

B<NOTE:> Please note that the function described in this chapter have "SSL_" part stripped from their original openssl names.

=over

=item * new

Creates a new SSL structure which is needed to hold the data for a TLS/SSL connection.
The new structure inherits the settings of the underlying context $ctx: connection
method (SSLv2/v3/TLSv1), options, verification settings, timeout settings.

 my $rv = Net::SSLeay::new($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: value corresponding to openssl's SSL structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_new.html|http://www.openssl.org/docs/ssl/SSL_new.html>

=item * accept

Waits for a TLS/SSL client to initiate the TLS/SSL handshake. The communication
channel must already have been set and assigned to the ssl by setting an underlying BIO.

 my $rv = Net::SSLeay::accept($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: 1 = success, 0 = handshake not successful, <0 = fatal error during handshake

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_accept.html|http://www.openssl.org/docs/ssl/SSL_accept.html>

=item * add_client_CA

Adds the CA name extracted from cacert to the list of CAs sent to the client
when requesting a client certificate for the chosen ssl, overriding the setting
valid for ssl's SSL_CTX object.

 my $rv = Net::SSLeay::add_client_CA($ssl, $x);
 # $ssl - value corresponding to openssl's SSL structure
 # $x - value corresponding to openssl's X509 structure
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_client_CA_list.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_client_CA_list.html>

=item * callback_ctrl

??? (more info needed)

 my $rv = Net::SSLeay::callback_ctrl($ssl, $cmd, $fp);
 # $ssl - value corresponding to openssl's SSL structure
 # $cmd - (integer) command id
 # $fp - (function pointer) ???
 #
 # returns: ???

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_ctrl.html|http://www.openssl.org/docs/ssl/SSL_CTX_ctrl.html>

=item * check_private_key

Checks the consistency of a private key with the corresponding certificate loaded into $ssl

 my $rv = Net::SSLeay::check_private_key($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: 1 on success, otherwise check out the error stack to find out the reason

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html|http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

=item * clear

Reset SSL object to allow another connection.

 Net::SSLeay::clear($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_clear.html|http://www.openssl.org/docs/ssl/SSL_clear.html>

=item * connect

Initiate the TLS/SSL handshake with an TLS/SSL server.

 my $rv = Net::SSLeay::connect($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: 1 = success, 0 = handshake not successful, <0 = fatal error during handshake

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_connect.html|http://www.openssl.org/docs/ssl/SSL_connect.html>

=item * copy_session_id

Copies the session structure fro $from to $to (+ also the private key and certificate associated with $from).

 Net::SSLeay::copy_session_id($to, $from);
 # $to - value corresponding to openssl's SSL structure
 # $from - value corresponding to openssl's SSL structure
 #
 # returns: no return value

=item * ctrl

Internal handling function for SSL objects.

B<BEWARE:> openssl doc says: This function should never be called directly!

 my $rv = Net::SSLeay::ctrl($ssl, $cmd, $larg, $parg);
 # $ssl - value corresponding to openssl's SSL structure
 # $cmd - (integer) command id
 # $larg - (integer) long ???
 # $parg - (string/pointer) ???
 #
 # returns: (long) result of given command ???

For more details about valid $cmd values check L</CTX_ctrl>.

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_ctrl.html|http://www.openssl.org/docs/ssl/SSL_CTX_ctrl.html>

=item * do_handshake

Will wait for a SSL/TLS handshake to take place. If the connection is in client
mode, the handshake will be started. The handshake routines may have to be
explicitly set in advance using either SSL_set_connect_state or SSL_set_accept_state(3).

 my $rv = Net::SSLeay::do_handshake($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: 1 = success, 0 = handshake not successful, <0 = fatal error during handshake

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_do_handshake.html|http://www.openssl.org/docs/ssl/SSL_do_handshake.html>

=item * dup

Returns a duplicate of $ssl.

 my $rv = Net::SSLeay::dup($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: value corresponding to openssl's SSL structure (0 on failure)

=item * free

Free an allocated SSL structure.

 Net::SSLeay::free($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_free.html|http://www.openssl.org/docs/ssl/SSL_free.html>

=item * get0_param

B<COMPATIBILITY:> not available in Net-SSLeay-1.82 and before; requires at least OpenSSL 1.0.2

Returns the current verification parameters.

 my $vpm = Net::SSLeay::get0_param($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: value corresponding to openssl's X509_VERIFY_PARAM structure

Check openssl doc L<https://www.openssl.org/docs/ssl/SSL_CTX_get0_param.html|https://www.openssl.org/docs/ssl/SSL_CTX_get0_param.html>

=item * get_SSL_CTX

Returns a pointer to the SSL_CTX object, from which $ssl was created with Net::SSLeay::new.

 my $rv = Net::SSLeay::get_SSL_CTX($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: value corresponding to openssl's SSL_CTX structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_get_SSL_CTX.html|http://www.openssl.org/docs/ssl/SSL_get_SSL_CTX.html>

=item * set_SSL_CTX

Sets the SSL_CTX the corresponds to an SSL session.

 my $the_ssl_ctx = Net::SSLeay::set_SSL_CTX($ssl, $ssl_ctx);
 # $ssl - value corresponding to openssl's SSL structure
 # $ssl_ctx - Change the ssl object to the given ssl_ctx
 #
 # returns - the ssl_ctx

=item * get_app_data

Can be used to get application defined value/data.

 my $rv = Net::SSLeay::get_app_data($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: string/buffer/pointer ???

=item * set_app_data

Can be used to set some application defined value/data.

 my $rv = Net::SSLeay::set_app_data($ssl, $arg);
 # $ssl - value corresponding to openssl's SSL structure
 # $arg - (string/buffer/pointer ???) data
 #
 # returns: ???

=item * get_certificate

Gets X509 certificate from an established SSL connection.

 my $rv = Net::SSLeay::get_certificate($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: value corresponding to openssl's X509 structure (0 on failure)

=item * get_cipher

Obtains the name of the currently used cipher.

 my $rv = Net::SSLeay::get_cipher($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: (string) cipher name e.g. 'DHE-RSA-AES256-SHA' or '', when no session has been established.

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_get_current_cipher.html|http://www.openssl.org/docs/ssl/SSL_get_current_cipher.html>

=item * get_cipher_bits

Obtain the number of secret/algorithm bits used.

 my $rv = Net::SSLeay::get_cipher_bits($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: number of secret bits used by current cipher

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_get_current_cipher.html|http://www.openssl.org/docs/ssl/SSL_get_current_cipher.html>
and L<http://www.openssl.org/docs/ssl/SSL_CIPHER_get_name.html|http://www.openssl.org/docs/ssl/SSL_CIPHER_get_name.html>

=item * get_cipher_list

Returns the name (string) of the SSL_CIPHER listed for $ssl with priority $n.

 my $rv = Net::SSLeay::get_cipher_list($ssl, $n);
 # $ssl - value corresponding to openssl's SSL structure
 # $n - (integer) priority
 #
 # returns: (string) cipher name e.g. 'EDH-DSS-DES-CBC3-SHA' or '' in case of error

Call Net::SSLeay::get_cipher_list with priority starting from 0 to obtain
the sorted list of available ciphers, until '' is returned:

 my $priority = 0;
 while (my $c = Net::SSLeay::get_cipher_list($ssl, $priority)) {
   print "cipher[$priority] = $c\n";
   $priority++;
 }

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_get_ciphers.html|http://www.openssl.org/docs/ssl/SSL_get_ciphers.html>

=item * get_client_CA_list

Returns the list of client CAs explicitly set for $ssl using C<Net::SSleay::set_client_CA_list>
or $ssl's SSL_CTX object with C<Net::SSLeay::CTX_set_client_CA_list>, when in server mode.

In client mode, returns the list of client CAs sent from the server, if any.

 my $rv = Net::SSLeay::get_client_CA_list($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: value corresponding to openssl's STACK_OF(X509_NAME) structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_get_client_CA_list.html|http://www.openssl.org/docs/ssl/SSL_get_client_CA_list.html>

=item * get_current_cipher

Returns the cipher actually used.

 my $rv = Net::SSLeay::get_current_cipher($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: value corresponding to openssl's SSL_CIPHER structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_get_current_cipher.html|http://www.openssl.org/docs/ssl/SSL_get_current_cipher.html>

=item * get_default_timeout

Returns the default timeout value assigned to SSL_SESSION objects negotiated for the protocol valid for $ssl.

 my $rv = Net::SSLeay::get_default_timeout($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: (long) timeout in seconds

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_get_default_timeout.html|http://www.openssl.org/docs/ssl/SSL_get_default_timeout.html>

=item * get_error

Returns a result code for a preceding call to C<connect>, C<accept>, C<do_handshake>, C<read>, C<peek> or C<write> on $ssl.

 my $rv = Net::SSLeay::get_error($ssl, $ret);
 # $ssl - value corresponding to openssl's SSL structure
 # $ret - return value of preceding TLS/SSL I/O operation
 #
 # returns: result code, which is one of the following values:
 #  0 - SSL_ERROR_NONE
 #  1 - SSL_ERROR_SSL
 #  2 - SSL_ERROR_WANT_READ
 #  3 - SSL_ERROR_WANT_WRITE
 #  4 - SSL_ERROR_WANT_X509_LOOKUP
 #  5 - SSL_ERROR_SYSCALL
 #  6 - SSL_ERROR_ZERO_RETURN
 #  7 - SSL_ERROR_WANT_CONNECT
 #  8 - SSL_ERROR_WANT_ACCEPT

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_get_error.html|http://www.openssl.org/docs/ssl/SSL_get_error.html>

=item * get_ex_data

Is used to retrieve the information for $idx from $ssl.

 my $rv = Net::SSLeay::get_ex_data($ssl, $idx);
 # $ssl - value corresponding to openssl's SSL structure
 # $idx - (integer) index for application specific data
 #
 # returns: pointer to ???

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_get_ex_new_index.html|http://www.openssl.org/docs/ssl/SSL_get_ex_new_index.html>

=item * set_ex_data

Is used to store application data at $data for $idx into the $ssl object.

 my $rv = Net::SSLeay::set_ex_data($ssl, $idx, $data);
 # $ssl - value corresponding to openssl's SSL structure
 # $idx - (integer) ???
 # $data - (pointer) ???
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_get_ex_new_index.html|http://www.openssl.org/docs/ssl/SSL_get_ex_new_index.html>

=item * get_ex_new_index

Is used to register a new index for application specific data.

 my $rv = Net::SSLeay::get_ex_new_index($argl, $argp, $new_func, $dup_func, $free_func);
 # $argl - (long) ???
 # $argp - (pointer) ???
 # $new_func - function pointer ??? (CRYPTO_EX_new *)
 # $dup_func - function pointer ??? (CRYPTO_EX_dup *)
 # $free_func - function pointer ??? (CRYPTO_EX_free *)
 #
 # returns: (integer) ???

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_get_ex_new_index.html|http://www.openssl.org/docs/ssl/SSL_get_ex_new_index.html>

=item * get_fd

Returns the file descriptor which is linked to $ssl.

 my $rv = Net::SSLeay::get_fd($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: file descriptor (>=0) or -1 on failure

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_get_fd.html|http://www.openssl.org/docs/ssl/SSL_get_fd.html>

=item * get_finished

Obtains the latest 'Finished' message sent to the peer. Return value
is zero if there's been no Finished message yet. Default count is
2*EVP_MAX_MD_SIZE that is long enough for all possible Finish
messages. If you supply a non-default count, the resulting return
value may be longer than returned buf's length.

 my $rv = Net::SSLeay::get_finished($ssl, $buf, $count);
 # $ssl - value corresponding to openssl's SSL structure
 # $buf - buffer where the returned data will be stored
 # $count - [optional] max size of return data - default is 2*EVP_MAX_MD_SIZE
 #
 # returns: length of latest Finished message

=item * get_peer_finished

Obtains the latest 'Finished' message expected from the
peer. Parameters and return value are similar to get_finished().

 my $rv = Net::SSLeay::get_peer_finished($ssl, $buf, $count);
 # $ssl - value corresponding to openssl's SSL structure
 # $buf - buffer where the returned data will be stored
 # $count - [optional] max size of return data - default is 2*EVP_MAX_MD_SIZE
 #
 # returns: length of latest Finished message

=item * get_keyblock_size

Gets the length of the TLS keyblock.

B<NOTE:> Does not exactly correspond to any low level API function.

 my $rv = Net::SSLeay::get_keyblock_size($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: keyblock size, -1 on error

=item * get_mode

Returns the mode (bitmask) set for $ssl.

 my $rv = Net::SSLeay::get_mode($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: mode (bitmask)

To decode the return value (bitmask) see documentation for L</CTX_get_mode>.

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_mode.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_mode.html>

=item * set_mode

Adds the mode set via bitmask in $mode to $ssl. Options already set before are not cleared.

 my $rv = Net::SSLeay::set_mode($ssl, $mode);
 # $ssl - value corresponding to openssl's SSL structure
 # $mode - mode (bitmask)
 #
 # returns: the new mode bitmask after adding $mode

For $mode bitmask details see L</CTX_get_mode>.

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_mode.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_mode.html>

=item * get_options

Returns the options (bitmask) set for $ssl.

 my $rv = Net::SSLeay::get_options($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: options (bitmask)

To decode the return value (bitmask) see documentation for L</CTX_get_options>.

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_options.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_options.html>

=item * set_options

Adds the options set via bitmask in $options to $ssl. Options already set before are not cleared!

 Net::SSLeay::set_options($ssl, $options);
 # $ssl - value corresponding to openssl's SSL structure
 # $options - options (bitmask)
 #
 # returns: the new options bitmask after adding $options

For $options bitmask details see L</CTX_get_options>.

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_options.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_options.html>

=item * get_peer_certificate

Get the X509 certificate of the peer.

 my $rv = Net::SSLeay::get_peer_certificate($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: value corresponding to openssl's X509 structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_get_peer_certificate.html|http://www.openssl.org/docs/ssl/SSL_get_peer_certificate.html>

=item * get_peer_cert_chain

Get the certificate chain of the peer as an array of X509 structures.

 my @rv = Net::SSLeay::get_peer_cert_chain($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: list of X509 structures

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_get_peer_certificate.html|http://www.openssl.org/docs/ssl/SSL_get_peer_certificate.html>

=item * get_quiet_shutdown

Returns the 'quiet shutdown' setting of ssl.

 my $rv = Net::SSLeay::get_quiet_shutdown($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: (integer) current 'quiet shutdown' value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_quiet_shutdown.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_quiet_shutdown.html>

=item * get_rbio

Get 'read' BIO linked to an SSL object $ssl.

 my $rv = Net::SSLeay::get_rbio($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: value corresponding to openssl's BIO structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_get_rbio.html|http://www.openssl.org/docs/ssl/SSL_get_rbio.html>

=item * get_read_ahead

 my $rv = Net::SSLeay::get_read_ahead($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: (integer) read_ahead value

=item * set_read_ahead

 Net::SSLeay::set_read_ahead($ssl, $val);
 # $ssl - value corresponding to openssl's SSL structure
 # $val - read_ahead value to be set
 #
 # returns: the original read_ahead value

=item * get_security_level

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.0, not in LibreSSL

Returns the security level associated with $ssl.

 my $level = Net::SSLeay::get_security_level($ssl);
 # $ssl   - value corresponding to openssl's SSL structure
 #
 # returns: (integer) current security level

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_get_security_level.html|https://www.openssl.org/docs/manmaster/man3/SSL_get_security_level.html>

=item * set_security_level

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.0, not in LibreSSL

Sets the security level associated with $ssl to $level.

 Net::SSLeay::set_security_level($ssl, $level);
 # $ssl   - value corresponding to openssl's SSL structure
 # $level - new security level
 #
 # returns: no return value

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_set_security_level.html|https://www.openssl.org/docs/manmaster/man3/SSL_set_security_level.html>

=item * set_num_tickets

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.1, not in LibreSSL

Set number of TLSv1.3 session tickets that will be sent to a client.

 my $rv = Net::SSLeay::set_num_tickets($ssl, $number_of_tickets);
 # $ssl  - value corresponding to openssl's SSL structure
 # $number_of_tickets - number of tickets to send
 #
 # returns: 1 on success, 0 on failure

Set to zero if you do not no want to support a session resumption.

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_set_num_tickets.html|https://www.openssl.org/docs/manmaster/man3/SSL_set_num_tickets.html>

=item * get_num_tickets

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.1, not in LibreSSL

Get number of TLSv1.3 session tickets that will be sent to a client.

 my $number_of_tickets = Net::SSLeay::get_num_tickets($ctx);
 # $ctx  - value corresponding to openssl's SSL structure
 #
 # returns: number of tickets to send

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_get_num_tickets.html|https://www.openssl.org/docs/manmaster/man3/SSL_get_num_tickets.html>

=item * get_server_random

Returns internal SSLv3 server_random value.

 Net::SSLeay::get_server_random($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: server_random value (binary data)

=item * get_client_random

B<NOTE:> Does not exactly correspond to any low level API function

Returns internal SSLv3 client_random value.

 Net::SSLeay::get_client_random($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: client_random value (binary data)

=item * export_keying_material

Returns keying material based on the string $label and optional
$context. Note that with TLSv1.2 and lower, empty context (empty
string) and undefined context (no value or 'undef') will return
different values.

  my $out = Net::SSLeay::export_keying_material($ssl, $olen, $label, $context);
  # $ssl - value corresponding to openssl's SSL structure
  # $olen - number of bytes to return
  # $label - application specific label
  # $context - [optional] context - default is undef for no context
  #
  # returns: keying material (binary data) or undef on error

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_export_keying_material.html|https://www.openssl.org/docs/manmaster/man3/SSL_export_keying_material.html>

=item * get_session

Retrieve TLS/SSL session data used in $ssl. The reference count of the SSL_SESSION is NOT incremented.

 my $rv = Net::SSLeay::get_session($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: value corresponding to openssl's SSL_SESSION structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_get_session.html|http://www.openssl.org/docs/ssl/SSL_get_session.html>

=item * SSL_get0_session

The alias for L</get_session> (note that the name is C<SSL_get0_session> NOT C<get0_session>).

 my $rv = Net::SSLeay::SSL_get0_session();

=item * get1_session

Returns a pointer to the SSL_SESSION actually used in $ssl. The reference count of the SSL_SESSION is incremented by 1.

 my $rv = Net::SSLeay::get1_session($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: value corresponding to openssl's SSL_SESSION structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_get_session.html|http://www.openssl.org/docs/ssl/SSL_get_session.html>

=item * get_shared_ciphers

Returns string with a list (colon ':' separated) of ciphers shared between client and server
within SSL session $ssl.

 my $rv = Net::SSLeay::get_shared_ciphers()
 #
 # returns: string like 'ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES256-SHA:DHE-DSS-AES256-SHA:...'

=item * get_shutdown

Returns the shutdown mode of $ssl.

 my $rv = Net::SSLeay::get_shutdown($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: shutdown mode (bitmask) of ssl

 #to decode the return value (bitmask) use:
 0 - No shutdown setting, yet
 1 - SSL_SENT_SHUTDOWN
 2 - SSL_RECEIVED_SHUTDOWN

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_set_shutdown.html|http://www.openssl.org/docs/ssl/SSL_set_shutdown.html>

=item * get_ssl_method

Returns a function pointer to the TLS/SSL method set in $ssl.

 my $rv = Net::SSLeay::get_ssl_method($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: value corresponding to openssl's SSL_METHOD structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_ssl_version.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_ssl_version.html>

=item * in_init, in_before, is_init_finished, in_connect_init, in_accept_init

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before.

Retrieve information about the handshake state machine. All functions take $ssl as the only argument and return 0 or 1. These functions are recommended over get_state() and state().

 my $rv = Net::SSLeay::is_init_finished($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: All functions return 1 or 0

Check openssl doc L<https://www.openssl.org/docs/ssl/SSL_in_init.html|http://www.openssl.org/docs/ssl/SSL_in_init.html>

=item * get_state

B<COMPATIBILITY:> OpenSSL 1.1.0 and later use different constants which are not made available. Use is_init_finished() and related functions instead.

Returns the SSL connection state.

 my $rv = Net::SSLeay::get_state($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: (integer) state value
 #          to decode the returned state check:
 #          SSL_ST_* constants in openssl/ssl.h
 #          SSL2_ST_* constants in openssl/ssl2.h
 #          SSL23_ST_* constants in openssl/ssl23.h
 #          SSL3_ST_* + DTLS1_ST_* constants in openssl/ssl3.h

=item * state

Exactly the same as L</get_state>.

 my $rv = Net::SSLeay::state($ssl);

=item * set_state

Sets the SSL connection state.

 Net::SSLeay::set_state($ssl,Net::SSLeay::SSL_ST_ACCEPT());

Not available with OpenSSL 1.1 and later.

=item * get_verify_depth

Returns the verification depth limit currently set in $ssl.

 my $rv = Net::SSLeay::get_verify_depth($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: current depth or -1 if no limit has been explicitly set

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_get_verify_mode.html|http://www.openssl.org/docs/ssl/SSL_CTX_get_verify_mode.html>

=item * set_verify_depth

Sets the maximum depth for the certificate chain verification that shall be allowed for $ssl.

 Net::SSLeay::set_verify_depth($ssl, $depth);
 # $ssl - value corresponding to openssl's SSL structure
 # $depth - (integer) depth
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_verify.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_verify.html>

=item * get_verify_mode

Returns the verification mode (bitmask) currently set in $ssl.

 my $rv = Net::SSLeay::get_verify_mode($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: mode (bitmask)

To decode the return value (bitmask) see documentation for L</CTX_get_verify_mode>.

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_get_verify_mode.html|http://www.openssl.org/docs/ssl/SSL_CTX_get_verify_mode.html>

=item * set_verify

Sets the verification flags for $ssl to be $mode and specifies the $verify_callback function to be used.

 Net::SSLeay::set_verify($ssl, $mode, $callback);
 # $ssl - value corresponding to openssl's SSL structure
 # $mode - mode (bitmask)
 # $callback - [optional] reference to perl callback function
 #
 # returns: no return value

For $mode bitmask details see L</CTX_get_verify_mode>.

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_verify.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_verify.html>

=item * set_post_handshake_auth

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.1, not in LibreSSL

Enable the Post-Handshake Authentication extension to be added to the ClientHello such that post-handshake authentication can be requested by the server.

 Net::SSLeay::set_posthandshake_auth($ssl, $val);
 # $ssl - value corresponding to openssl's SSL structure
 # $val - 0 then the extension is not sent, otherwise it is
 #
 # returns: no return value

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_set_post_handshake_auth|https://www.openssl.org/docs/manmaster/man3/SSL_set_post_handshake_auth.html>

=item * verify_client_post_handshake

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.1, not in LibreSSL

verify_client_post_handshake causes a CertificateRequest message to be sent by a server on the given ssl connection.

 my $rv = Net::SSLeay::verify_client_post_handshake($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: 1 if the request succeeded, and 0 if the request failed. The error stack can be examined to determine the failure reason.

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_verify_client_post_handshake.html|https://www.openssl.org/docs/manmaster/man3/SSL_verify_client_post_handshake.html>

=item * get_verify_result

Returns the result of the verification of the X509 certificate presented by the peer, if any.

 my $rv = Net::SSLeay::get_verify_result($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: (integer)
 #      0 - X509_V_OK: ok
 #      2 - X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT: unable to get issuer certificate
 #      3 - X509_V_ERR_UNABLE_TO_GET_CRL: unable to get certificate CRL
 #      4 - X509_V_ERR_UNABLE_TO_DECRYPT_CERT_SIGNATURE: unable to decrypt certificate's signature
 #      5 - X509_V_ERR_UNABLE_TO_DECRYPT_CRL_SIGNATURE: unable to decrypt CRL's signature
 #      6 - X509_V_ERR_UNABLE_TO_DECODE_ISSUER_PUBLIC_KEY: unable to decode issuer public key
 #      7 - X509_V_ERR_CERT_SIGNATURE_FAILURE: certificate signature failure
 #      8 - X509_V_ERR_CRL_SIGNATURE_FAILURE: CRL signature failure
 #      9 - X509_V_ERR_CERT_NOT_YET_VALID: certificate is not yet valid
 #     10 - X509_V_ERR_CERT_HAS_EXPIRED: certificate has expired
 #     11 - X509_V_ERR_CRL_NOT_YET_VALID: CRL is not yet valid
 #     12 - X509_V_ERR_CRL_HAS_EXPIRED: CRL has expired
 #     13 - X509_V_ERR_ERROR_IN_CERT_NOT_BEFORE_FIELD: format error in certificate's notBefore field
 #     14 - X509_V_ERR_ERROR_IN_CERT_NOT_AFTER_FIELD: format error in certificate's notAfter field
 #     15 - X509_V_ERR_ERROR_IN_CRL_LAST_UPDATE_FIELD: format error in CRL's lastUpdate field
 #     16 - X509_V_ERR_ERROR_IN_CRL_NEXT_UPDATE_FIELD: format error in CRL's nextUpdate field
 #     17 - X509_V_ERR_OUT_OF_MEM: out of memory
 #     18 - X509_V_ERR_DEPTH_ZERO_SELF_SIGNED_CERT: self signed certificate
 #     19 - X509_V_ERR_SELF_SIGNED_CERT_IN_CHAIN: self signed certificate in certificate chain
 #     20 - X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY: unable to get local issuer certificate
 #     21 - X509_V_ERR_UNABLE_TO_VERIFY_LEAF_SIGNATURE: unable to verify the first certificate
 #     22 - X509_V_ERR_CERT_CHAIN_TOO_LONG: certificate chain too long
 #     23 - X509_V_ERR_CERT_REVOKED: certificate revoked
 #     24 - X509_V_ERR_INVALID_CA: invalid CA certificate
 #     25 - X509_V_ERR_PATH_LENGTH_EXCEEDED: path length constraint exceeded
 #     26 - X509_V_ERR_INVALID_PURPOSE: unsupported certificate purpose
 #     27 - X509_V_ERR_CERT_UNTRUSTED: certificate not trusted
 #     28 - X509_V_ERR_CERT_REJECTED: certificate rejected
 #     29 - X509_V_ERR_SUBJECT_ISSUER_MISMATCH: subject issuer mismatch
 #     30 - X509_V_ERR_AKID_SKID_MISMATCH: authority and subject key identifier mismatch
 #     31 - X509_V_ERR_AKID_ISSUER_SERIAL_MISMATCH: authority and issuer serial number mismatch
 #     32 - X509_V_ERR_KEYUSAGE_NO_CERTSIGN:key usage does not include certificate signing
 #     50 - X509_V_ERR_APPLICATION_VERIFICATION: application verification failure

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_get_verify_result.html|http://www.openssl.org/docs/ssl/SSL_get_verify_result.html>

=item * set_verify_result

Override result of peer certificate verification.

 Net::SSLeay::set_verify_result($ssl, $v);
 # $ssl - value corresponding to openssl's SSL structure
 # $v - (integer) result value
 #
 # returns: no return value

For more info about valid return values see L</get_verify_result>

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_set_verify_result.html|http://www.openssl.org/docs/ssl/SSL_set_verify_result.html>

=item * get_wbio

Get 'write' BIO linked to an SSL object $ssl.

 my $rv = Net::SSLeay::get_wbio($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: value corresponding to openssl's BIO structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_get_rbio.html|http://www.openssl.org/docs/ssl/SSL_get_rbio.html>

=item * load_client_CA_file

Load X509 certificates from file (PEM formatted).

 my $rv = Net::SSLeay::load_client_CA_file($file);
 # $file - (string) file name
 #
 # returns: value corresponding to openssl's STACK_OF(X509_NAME) structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_load_client_CA_file.html|http://www.openssl.org/docs/ssl/SSL_load_client_CA_file.html>

=item * clear_num_renegotiations

Executes SSL_CTRL_CLEAR_NUM_RENEGOTIATIONS command on $ssl.

 my $rv = Net::SSLeay::clear_num_renegotiations($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: command result

=item * need_tmp_RSA

Executes SSL_CTRL_NEED_TMP_RSA command on $ssl.

 my $rv = Net::SSLeay::need_tmp_RSA($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: command result

Not available with OpenSSL 1.1 and later.

=item * num_renegotiations

Executes SSL_CTRL_GET_NUM_RENEGOTIATIONS command on $ssl.

 my $rv = Net::SSLeay::num_renegotiations($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: command result

=item * total_renegotiations

Executes SSL_CTRL_GET_TOTAL_RENEGOTIATIONS command on $ssl.

 my $rv = Net::SSLeay::total_renegotiations($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: command result

=item * peek

Copies $max bytes from the specified $ssl into the returned value.
In contrast to the C<Net::SSLeay::read()> function, the data in the SSL
buffer is unmodified after the SSL_peek() operation.

 Net::SSLeay::peek($ssl, $max);
 # $ssl - value corresponding to openssl's SSL structure
 # $max - [optional] max bytes to peek (integer) - default is 32768
 #
 # in scalar context: data read from the TLS/SSL connection, undef on error
 # in list context:   two-item array consisting of data read (undef on error),
 #                      and return code from SSL_peek().

=item * peek_ex

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.1, not in LibreSSL

Copies $max bytes from the specified $ssl into the returned value.
In contrast to the C<Net::SSLeay::read_ex()> function, the data in the SSL
buffer is unmodified after the SSL_peek_ex() operation.

 my($got, $rv) = Net::SSLeay::peek_ex($ssl, $max);
 # $ssl - value corresponding to openssl's SSL structure
 # $max - [optional] max bytes to peek (integer) - default is 32768
 #
 # returns a list: two-item list consisting of data read (undef on error),
 #                 and return code from SSL_peek_ex().

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_peek_ex.html|https://www.openssl.org/docs/manmaster/man3/SSL_peek_ex.html>

=item * pending

Obtain number of readable bytes buffered in $ssl object.

 my $rv = Net::SSLeay::pending($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: the number of bytes pending

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_pending.html|http://www.openssl.org/docs/ssl/SSL_pending.html>

=item * has_pending

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.0, not in LibreSSL

Returns 1 if $ssl has buffered data (whether processed or unprocessed) and 0 otherwise.

 my $rv = Net::SSLeay::has_pending($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: (integer) 1 or 0

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_has_pending.html|https://www.openssl.org/docs/manmaster/man3/SSL_has_pending.html>

=item * read

Tries to read $max bytes from the specified $ssl.

 my $got = Net::SSLeay::read($ssl, $max);
 my($got, $rv) = Net::SSLeay::read($ssl, $max);
 # $ssl - value corresponding to openssl's SSL structure
 # $max - [optional] max bytes to read (integer) - default is 32768
 #
 # returns:
 # in scalar context: data read from the TLS/SSL connection, undef on error
 # in list context:   two-item array consisting of data read (undef on error),
 #                      and return code from SSL_read().

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_read.html|http://www.openssl.org/docs/ssl/SSL_read.html>

=item * read_ex

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.1, not in LibreSSL

Tries to read $max bytes from the specified $ssl.

 my($got, $rv) = Net::SSLeay::read_ex($ssl, $max);
 # $ssl - value corresponding to openssl's SSL structure
 # $max - [optional] max bytes to read (integer) - default is 32768
 #
 # returns a list: two-item list consisting of data read (undef on error),
 #                 and return code from SSL_read_ex().

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_read_ex.html|https://www.openssl.org/docs/manmaster/man3/SSL_read_ex.html>

=item * renegotiate

Turn on flags for renegotiation so that renegotiation will happen

 my $rv = Net::SSLeay::renegotiate($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: 1 on success, 0 on failure

=item * rstate_string

Returns a 2 letter string indicating the current read state of the SSL object $ssl.

 my $rv = Net::SSLeay::rstate_string($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: 2-letter string

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_rstate_string.html|http://www.openssl.org/docs/ssl/SSL_rstate_string.html>

=item * rstate_string_long

Returns a string indicating the current read state of the SSL object ssl.

 my $rv = Net::SSLeay::rstate_string_long($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: string with current state

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_rstate_string.html|http://www.openssl.org/docs/ssl/SSL_rstate_string.html>

=item * session_reused

Query whether a reused session was negotiated during handshake.

 my $rv = Net::SSLeay::session_reused($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: 0 - new session was negotiated; 1 - session was reused.

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_session_reused.html|http://www.openssl.org/docs/ssl/SSL_session_reused.html>

=item * set1_param

Applies X509 verification parameters $vpm on $ssl

 my $rv = Net::SSLeay::set1_param($ssl, $vpm);
 # $ssl - value corresponding to openssl's SSL structure
 # $vpm - value corresponding to openssl's X509_VERIFY_PARAM structure
 #
 # returns: 1 on success, 0 on failure

=item * set_accept_state

Sets $ssl to work in server mode.

 Net::SSLeay::set_accept_state($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_set_connect_state.html|http://www.openssl.org/docs/ssl/SSL_set_connect_state.html>

=item * set_bio

Connects the BIOs $rbio and $wbio for the read and write operations of the TLS/SSL (encrypted) side of $ssl.

 Net::SSLeay::set_bio($ssl, $rbio, $wbio);
 # $ssl - value corresponding to openssl's SSL structure
 # $rbio - value corresponding to openssl's BIO structure
 # $wbio - value corresponding to openssl's BIO structure
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_set_bio.html|http://www.openssl.org/docs/ssl/SSL_set_bio.html>

=item * set_cipher_list

Sets the list of ciphers only for ssl.

 my $rv = Net::SSLeay::set_cipher_list($ssl, $str);
 # $ssl - value corresponding to openssl's SSL structure
 # $str - (string) cipher list e.g. '3DES:+RSA'
 #
 # returns: 1 if any cipher could be selected and 0 on complete failure

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_cipher_list.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_cipher_list.html>

=item * set_ciphersuites

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.1, not in LibreSSL

Configure the available TLSv1.3 ciphersuites.

 my $rv = Net::SSLeay::set_ciphersuites($ssl, $str);
 # $ssl  - value corresponding to openssl's SSL structure
 # $str  - colon (":") separated list of TLSv1.3 ciphersuite names in order of preference
 #
 # returns: (integer) 1 if the requested ciphersuite list was configured, and 0 otherwise

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_set_ciphersuites.html|https://www.openssl.org/docs/manmaster/man3/SSL_set_ciphersuites.html>

=item * set_client_CA_list

Sets the list of CAs sent to the client when requesting a client certificate
for the chosen $ssl, overriding the setting valid for $ssl's SSL_CTX object.

 my $rv = Net::SSLeay::set_client_CA_list($ssl, $list);
 # $ssl - value corresponding to openssl's SSL structure
 # $list - value corresponding to openssl's STACK_OF(X509_NAME) structure
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_client_CA_list.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_client_CA_list.html>

=item * set_connect_state

Sets $ssl to work in client mode.

 Net::SSLeay::set_connect_state($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_set_connect_state.html|http://www.openssl.org/docs/ssl/SSL_set_connect_state.html>

=item * set_fd

Sets the file descriptor $fd as the input/output facility for the TLS/SSL (encrypted)
side of $ssl, $fd will typically be the socket file descriptor of a network connection.

 my $rv = Net::SSLeay::set_fd($ssl, $fd);
 # $ssl - value corresponding to openssl's SSL structure
 # $fd - (integer) file handle (got via perl's fileno)
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_set_fd.html|http://www.openssl.org/docs/ssl/SSL_set_fd.html>

=item * set_psk_client_callback

Sets the psk client callback.

 Net::SSLeay::set_psk_client_callback($ssl, sub { my $hint = shift; return ($identity, $key) } );
 # $ssl - value corresponding to openssl's SSL structure
 # $hint - PSK identity hint send by the server
 # $identity - PSK identity
 # $key - PSK key, hex string without the leading '0x', e.g. 'deadbeef'
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_set_psk_client_callback.html|http://www.openssl.org/docs/ssl/SSL_set_psk_client_callback.html>

=item * set_rfd

Sets the file descriptor $fd as the input (read) facility for the TLS/SSL (encrypted) side of $ssl.

 my $rv = Net::SSLeay::set_rfd($ssl, $fd);
 # $ssl - value corresponding to openssl's SSL structure
 # $fd - (integer) file handle (got via perl's fileno)
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_set_fd.html|http://www.openssl.org/docs/ssl/SSL_set_fd.html>

=item * set_wfd

 my $rv = Net::SSLeay::set_wfd($ssl, $fd);
 # $ssl - value corresponding to openssl's SSL structure
 # $fd - (integer) file handle (got via perl's fileno)
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_set_fd.html|http://www.openssl.org/docs/ssl/SSL_set_fd.html>

=item * set_info_callback

Sets the callback function, that can be used to obtain state information for $ssl during connection setup and use.
When callback is undef, the callback setting currently valid for ctx is used.

 Net::SSLeay::set_info_callback($ssl, $cb, [$data]);
 # $ssl - value corresponding to openssl's SSL structure
 # $cb - sub { my ($ssl,$where,$ret,$data) = @_; ... }
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_info_callback.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_info_callback.html>

=item * CTX_set_info_callback

Sets the callback function on ctx, that can be used to obtain state information during ssl connection setup and use.
When callback is undef, an existing callback will be disabled.

 Net::SSLeay::CTX_set_info_callback($ssl, $cb, [$data]);
 # $ssl - value corresponding to openssl's SSL structure
 # $cb - sub { my ($ssl,$where,$ret,$data) = @_; ... }
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_info_callback.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_info_callback.html>

=item * set_pref_cipher

Sets the list of available ciphers for $ssl using the control string $str.

 my $rv = Net::SSLeay::set_pref_cipher($ssl, $str);
 # $ssl - value corresponding to openssl's SSL structure
 # $str - (string) cipher list e.g. '3DES:+RSA'
 #
 # returns: 1 if any cipher could be selected and 0 on complete failure

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_cipher_list.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_cipher_list.html>

=item * CTX_set_psk_client_callback

Sets the psk client callback.

 Net::SSLeay::CTX_set_psk_client_callback($ssl, sub { my $hint = shift; return ($identity, $key) } );
 # $ssl - value corresponding to openssl's SSL structure
 # $hint - PSK identity hint send by the server
 # $identity - PSK identity
 # $key - PSK key, hex string without the leading '0x', e.g. 'deadbeef'
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_psk_client_callback.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_psk_client_callback.html>

=item * set_purpose

 my $rv = Net::SSLeay::set_purpose($ssl, $purpose);
 # $ssl - value corresponding to openssl's SSL structure
 # $purpose - (integer) purpose identifier
 #
 # returns: 1 on success, 0 on failure

For more info about available $purpose identifiers see L</CTX_set_purpose>.

=item * set_quiet_shutdown

Sets the 'quiet shutdown' flag for $ssl to be $mode.

 Net::SSLeay::set_quiet_shutdown($ssl, $mode);
 # $ssl - value corresponding to openssl's SSL structure
 # $mode - 0 or 1
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_quiet_shutdown.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_quiet_shutdown.html>

=item * set_session

Set a TLS/SSL session to be used during TLS/SSL connect.

 my $rv = Net::SSLeay::set_session($to, $ses);
 # $to - value corresponding to openssl's SSL structure
 # $ses - value corresponding to openssl's SSL_SESSION structure
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_set_session.html|http://www.openssl.org/docs/ssl/SSL_set_session.html>

=item * set_session_id_context

Sets the context $sid_ctx of length $sid_ctx_len within which a session can be reused for the $ssl object.

 my $rv = Net::SSLeay::set_session_id_context($ssl, $sid_ctx, $sid_ctx_len);
 # $ssl - value corresponding to openssl's SSL structure
 # $sid_ctx - data buffer
 # $sid_ctx_len - length of data in $sid_ctx
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_session_id_context.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_session_id_context.html>

=item * set_session_secret_cb

Setup pre-shared secret session resumption function.

 Net::SSLeay::set_session_secret_cb($ssl, $func, $data);
 # $ssl - value corresponding to openssl's SSL structure
 # $func - perl reference to callback function
 # $data - [optional] data that will be passed to callback function when invoked
 #
 # returns: no return value

The callback function will be called like:
callback_function($secret, $ciphers, $pref_cipher, $data);

# $secret is the current master session key, usually all 0s at the beginning of a session
# $ciphers is ref to an array of peer cipher names
# $pref_cipher is a ref to an index into the list of cipher names of 
#  the preferred cipher. Set it if you want to specify a preferred cipher
# $data is the data passed to set_session_secret_cb

The callback function should return 1 if it likes the suggested cipher (or has selected an alternative 
by setting pref_cipher), else it should return 0 (in which case OpenSSL will select its own preferred cipher).

With OpenSSL 1.1 and later, callback_function can change the master key for the session by 
altering $secret and returning 1.

=item * CTX_set_tlsext_ticket_getkey_cb

Setup encryption for TLS session tickets (stateless session reuse).

 Net::SSLeay::CTX_set_tlsext_ticket_getkey_cb($ctx, $func, $data);
 # $ctx  - value corresponding to openssl's SSL_CTX structure
 # $func - perl reference to callback function
 # $data - [optional] data that will be passed to callback function when invoked
 #
 # returns: no return value

The callback function will be called like:
getkey($data,[$key_name]) -> ($key,$current_key_name)

# $data is the data passed to set_session_secret_cb
# $key_name is the name of the key OpenSSL has extracted from the session ticket
# $key is the requested key for ticket encryption + HMAC
# $current_key_name is the name for the currently valid key

OpenSSL will call the function without a key name if it generates a new ticket.
It then needs the callback to return the encryption+HMAC key and an identifier
(key name) for this key.

When OpenSSL gets a session ticket from the client it extracts the key name and
calls the callback with this name as argument. It then expects the callback to
return the encryption+HMAC key matching the requested key name and and also the
key name which should be used at the moment. If the requested key name and the
returned key name differ it means that this session ticket was created with an
expired key and need to be renewed. In this case OpenSSL will call the callback
again with no key name to create a new session ticket based on the old one.

The key must be at least 32 byte of random data which can be created with
RAND_bytes. Internally the first 16 byte are used as key in AES-128 encryption
while the next 16 byte are used for the SHA-256 HMAC.
The key name are binary data and must be exactly 16 byte long. 

Example:

    Net::SSLeay::RAND_bytes(my $oldkey,32);
    Net::SSLeay::RAND_bytes(my $newkey,32);
    my $oldkey_name = pack("a16",'oldsecret');
    my $newkey_name = pack("a16",'newsecret');

    my @keys = (
	[ $newkey_name, $newkey ], # current active key
	[ $oldkey_name, $oldkey ], # already expired
    );

    Net::SSLeay::CTX_set_tlsext_ticket_getkey_cb($server2->_ctx, sub {
	my ($mykeys,$name) = @_;

	# return (current_key, current_key_name) if no name given
	return ($mykeys->[0][1],$mykeys->[0][0]) if ! $name;

	# return (matching_key, current_key_name) if we find a key matching
	# the given name
	for(my $i = 0; $i<@$mykeys; $i++) {
	    next if $name ne $mykeys->[$i][0];
	    return ($mykeys->[$i][1],$mykeys->[0][0]);
	}

	# no matching key found
	return;
    },\@keys);


This function is based on the OpenSSL function SSL_CTX_set_tlsext_ticket_key_cb
but provides a simpler to use interface. For more information see
L<http://www.openssl.org/docs/ssl/SSL_CTX_set_tlsext_ticket_key_cb.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_tlsext_ticket_key_cb.html>

=item * set_session_ticket_ext_cb

Setup callback for TLS session tickets (stateless session reuse).

 Net::SSLeay::set_session_ticket_ext_cb($ssl, $func, $data);
 # $ssl  - value corresponding to openssl's SSL structure
 # $func - perl reference to callback function
 # $data - [optional] data that will be passed to callback function when invoked
 #
 # returns: no return value

The callback function will be called like:
getticket($ssl,$ticket,$data) -> $return_value

# $ssl is a value corresponding to openssl's SSL structure
# $ticket is a value of received TLS session ticket (can also be empty)
# $data is the data passed to set_session_ticket_ext_cb
# $return_value is either 0 (failure) or 1 (success)

This function is based on the OpenSSL function SSL_set_session_ticket_ext_cb.

=item * set_session_ticket_ext

Set TLS session ticket (stateless session reuse).

 Net::SSLeay::set_session_ticket_ext($ssl, $ticket);
 # $ssl    - value corresponding to openssl's SSL structure
 # $ticket - is a value of TLS session ticket which client will send (can also be empty string)
 #
 # returns: no return value

The callback function will be called like:
getticket($ssl,$ticket,$data) -> $return_value

# $ssl is a value corresponding to openssl's SSL structure
# $ticket is a value of received TLS session ticket (can also be empty)
# $data is the data passed to set_session_ticket_ext_cb
# $return_value is either 0 (failure) or 1 (success)

This function is based on the OpenSSL function SSL_set_session_ticket_ext_cb.

=item * set_shutdown

Sets the shutdown state of $ssl to $mode.

 Net::SSLeay::set_shutdown($ssl, $mode);
 # $ssl - value corresponding to openssl's SSL structure
 # $mode - (integer) shutdown mode:
 #         0 - No shutdown
 #         1 - SSL_SENT_SHUTDOWN
 #         2 - SSL_RECEIVED_SHUTDOWN
 #         3 - SSL_RECEIVED_SHUTDOWN+SSL_SENT_SHUTDOWN
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_set_shutdown.html|http://www.openssl.org/docs/ssl/SSL_set_shutdown.html>

=item * set_ssl_method

Sets a new TLS/SSL method for a particular $ssl object.

 my $rv = Net::SSLeay::set_ssl_method($ssl, $method);
 # $ssl - value corresponding to openssl's SSL structure
 # $method - value corresponding to openssl's SSL_METHOD structure
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_ssl_version.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_ssl_version.html>

=item * set_tmp_dh

Sets DH parameters to be used to be $dh.

 my $rv = Net::SSLeay::set_tmp_dh($ssl, $dh);
 # $ssl - value corresponding to openssl's SSL structure
 # $dh - value corresponding to openssl's DH structure
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_dh_callback.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_dh_callback.html>

=item * set_tmp_dh_callback

Sets the callback function for $ssl to be used when a DH parameters are required to $dh_cb.

??? (does this function really work?)

 Net::SSLeay::set_tmp_dh_callback($ssl, $dh);
 # $ssl - value corresponding to openssl's SSL structure
 # $dh_cb - pointer to function ???
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_dh_callback.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_dh_callback.html>

=item * set_tmp_rsa

Sets the temporary/ephemeral RSA key to be used in $ssl to be $rsa.

 my $rv = Net::SSLeay::set_tmp_rsa($ssl, $rsa);
 # $ssl - value corresponding to openssl's SSL structure
 # $rsa - value corresponding to openssl's RSA structure
 #
 # returns: 1 on success, 0 on failure

Example:

 $rsakey = Net::SSLeay::RSA_generate_key();
 Net::SSLeay::set_tmp_rsa($ssl, $rsakey);
 Net::SSLeay::RSA_free($rsakey);

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_rsa_callback.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_rsa_callback.html>

=item * set_tmp_rsa_callback

Sets the callback function for $ssl to be used when a temporary/ephemeral RSA key is required to $tmp_rsa_callback.

??? (does this function really work?)

 Net::SSLeay::set_tmp_rsa_callback($ssl, $tmp_rsa_callback);
 # $ssl - value corresponding to openssl's SSL structure
 # $tmp_rsa_callback - (function pointer) ???
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_rsa_callback.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_tmp_rsa_callback.html>

=item * set_trust

 my $rv = Net::SSLeay::set_trust($ssl, $trust);
 # $ssl - value corresponding to openssl's SSL structure
 # $trust - (integer) trust identifier
 #
 # returns: the original value

For more details about $trust values see L</CTX_set_trust>.

=item * shutdown

Shuts down an active TLS/SSL connection. It sends the 'close notify' shutdown alert to the peer.

 my $rv = Net::SSLeay::shutdown($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: 1 - shutdown was successfully completed
 #          0 - shutdown is not yet finished,
 #         -1 - shutdown was not successful

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_shutdown.html|http://www.openssl.org/docs/ssl/SSL_shutdown.html>

=item * state_string

Returns a 6 letter string indicating the current state of the SSL object $ssl.

 my $rv = Net::SSLeay::state_string($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: 6-letter string

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_state_string.html|http://www.openssl.org/docs/ssl/SSL_state_string.html>

=item * state_string_long

Returns a string indicating the current state of the SSL object $ssl.

 my $rv = Net::SSLeay::state_string_long($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: state strings

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_state_string.html|http://www.openssl.org/docs/ssl/SSL_state_string.html>

=item * set_default_passwd_cb

B<COMPATIBILITY:> not available in Net-SSLeay-1.82 and before; requires at least OpenSSL 1.1.0f. Not needed with LibreSSL.

Sets the default password callback called when loading/storing a PEM certificate with encryption for $ssl.

 Net::SSLeay::set_default_passwd_cb($ssl, $func);
 # $ssl - value corresponding to openssl's SSL structure
 # $func - perl reference to callback function
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_default_passwd_cb.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_default_passwd_cb.html>

=item * set_default_passwd_cb_userdata

B<COMPATIBILITY:> not available in Net-SSLeay-1.82 and before; requires at least OpenSSL 1.1.0f. Not needed with LibreSSL.

Sets a pointer to userdata which will be provided to the password callback of $ssl on invocation.

 Net::SSLeay::set_default_passwd_cb_userdata($ssl, $userdata);
 # $ssl - value corresponding to openssl's SSL structure
 # $userdata - data that will be passed to callback function when invoked
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_set_default_passwd_cb.html|http://www.openssl.org/docs/ssl/SSL_CTX_set_default_passwd_cb.html>

=item * use_PrivateKey

Adds $pkey as private key to $ssl.

 my $rv = Net::SSLeay::use_PrivateKey($ssl, $pkey);
 # $ssl - value corresponding to openssl's SSL structure
 # $pkey - value corresponding to openssl's EVP_PKEY structure
 #
 # returns: 1 on success, otherwise check out the error stack to find out the reason

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html|http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

=item * use_PrivateKey_ASN1

Adds the private key of type $pk stored in $data to $ssl.

 my $rv = Net::SSLeay::use_PrivateKey_ASN1($pk, $ssl, $d, $len);
 # $pk - (integer) key type, NID of corresponding algorithm
 # $ssl - value corresponding to openssl's SSL structure
 # $data - key data (binary)
 # $len - length of $data
 #
 # returns: 1 on success, otherwise check out the error stack to find out the reason

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html|http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

=item * use_PrivateKey_file

Adds the first private key found in $file to $ssl.

 my $rv = Net::SSLeay::use_PrivateKey_file($ssl, $file, $type);
 # $ssl - value corresponding to openssl's SSL structure
 # $file - (string) file name
 # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
 #
 # returns: 1 on success, otherwise check out the error stack to find out the reason

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html|http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

=item * use_RSAPrivateKey

Adds $rsa as RSA private key to $ssl.

 my $rv = Net::SSLeay::use_RSAPrivateKey($ssl, $rsa);
 # $ssl - value corresponding to openssl's SSL structure
 # $rsa - value corresponding to openssl's RSA structure
 #
 # returns: 1 on success, otherwise check out the error stack to find out the reason

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html|http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

=item * use_RSAPrivateKey_ASN1

Adds RSA private key stored in $data to $ssl.

 my $rv = Net::SSLeay::use_RSAPrivateKey_ASN1($ssl, $data, $len);
 # $ssl - value corresponding to openssl's SSL structure
 # $data - key data (binary)
 # $len - length of $data
 #
 # returns: 1 on success, otherwise check out the error stack to find out the reason

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html|http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

=item * use_RSAPrivateKey_file

Adds the first RSA private key found in $file to $ssl.

 my $rv = Net::SSLeay::use_RSAPrivateKey_file($ssl, $file, $type);
 # $ssl - value corresponding to openssl's SSL structure
 # $file - (string) file name
 # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
 #
 # returns: 1 on success, otherwise check out the error stack to find out the reason

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html|http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

=item * use_certificate

Loads the certificate $x into $ssl.

 my $rv = Net::SSLeay::use_certificate($ssl, $x);
 # $ssl - value corresponding to openssl's SSL structure
 # $x - value corresponding to openssl's X509 structure
 #
 # returns: 1 on success, otherwise check out the error stack to find out the reason

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html|http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

=item * use_certificate_ASN1

Loads the ASN1 encoded certificate from $data to $ssl.

 my $rv = Net::SSLeay::use_certificate_ASN1($ssl, $data, $len);
 # $ssl - value corresponding to openssl's SSL structure
 # $data - certificate data (binary)
 # $len - length of $data
 #
 # returns: 1 on success, otherwise check out the error stack to find out the reason

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html|http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

=item * use_certificate_chain_file

B<COMPATIBILITY>: not available in Net-SSLeay-1.82 and before; requires at least OpenSSL 1.1.0

Loads a certificate chain from $file into $ssl. The certificates must be in PEM format and must be sorted
starting with the subject's certificate (actual client or server certificate), followed by intermediate
CA certificates if applicable, and ending at the highest level (root) CA.

 my $rv = Net::SSLeay::use_certificate_chain_file($ssl, $file);
 # $ssl - value corresponding to openssl's SSL structure
 # $file - (string) file name
 #
 # returns: 1 on success, otherwise check out the error stack to find out the reason

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html|http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

=item * use_certificate_file

Loads the first certificate stored in $file into $ssl.

 my $rv = Net::SSLeay::use_certificate_file($ssl, $file, $type);
 # $ssl - value corresponding to openssl's SSL structure
 # $file - (string) file name
 # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
 #
 # returns: 1 on success, otherwise check out the error stack to find out the reason

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html|http://www.openssl.org/docs/ssl/SSL_CTX_use_certificate.html>

=item * get_version

Returns SSL/TLS protocol name

 my $rv = Net::SSLeay::get_version($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: (string) protocol name, see OpenSSL manual for the full list
 #          TLSv1
 #          TLSv1.3

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_get_version.html|https://www.openssl.org/docs/manmaster/man3/SSL_get_version.html>

=item * version

Returns SSL/TLS protocol version

 my $rv = Net::SSLeay::version($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: (integer) protocol version, see OpenSSL manual for the full list
 #          0x0301 - TLS1_VERSION  (TLSv1)
 #          0xFEFF - DTLS1_VERSION (DTLSv1)

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_version.html|https://www.openssl.org/docs/manmaster/man3/SSL_version.html>

=item * client_version

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.0, not in LibreSSL

Returns TLS protocol version used by the client when initiating the connection

 my $rv = Net::SSLeay::client_version($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: (integer) protocol version, see OpenSSL manual for the full list
 #          0x0301 - TLS1_VERSION  (TLSv1)
 #          0xFEFF - DTLS1_VERSION (DTLSv1)

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_client_version.html|https://www.openssl.org/docs/manmaster/man3/SSL_client_version.html>

=item * is_dtls

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.0, not in LibreSSL

 my $rv = Net::SSLeay::is_dtls($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: (integer) zero or one
 #          0 - connection is not using DTLS
 #          1 - connection is using DTLS

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_is_dtls.html|https://www.openssl.org/docs/manmaster/man3/SSL_is_dtls.html>

=item * want

Returns state information for the SSL object $ssl.

 my $rv = Net::SSLeay::want($ssl);
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: state
 #          1 - SSL_NOTHING
 #          2 - SSL_WRITING
 #          3 - SSL_READING
 #          4 - SSL_X509_LOOKUP

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_want.html|http://www.openssl.org/docs/ssl/SSL_want.html>

=item * write

Writes data from the buffer $data into the specified $ssl connection.

 my $rv = Net::SSLeay::write($ssl, $data);
 # $ssl - value corresponding to openssl's SSL structure
 # $data - data to be written
 #
 # returns: >0 - (success) number of bytes actually written to the TLS/SSL connection
 #           0 - write not successful, probably the underlying connection was closed
 #          <0 - error

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_write.html|http://www.openssl.org/docs/ssl/SSL_write.html>

=item * write_ex

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.1, not in LibreSSL

Writes data from the buffer $data into the specified $ssl connection.

 my ($len, $rv) = Net::SSLeay::write_ex($ssl, $data);
 # $ssl - value corresponding to openssl's SSL structure
 # $data - data to be written
 #
 # returns a list: two-item list consisting of number of bytes written,
 #                 and return code from SSL_write_ex()

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/SSL_write_ex.html|https://www.openssl.org/docs/manmaster/man3/SSL_write_ex.html>

=item * write_partial

B<NOTE:> Does not exactly correspond to any low level API function

Writes a fragment of data in $data from the buffer $data into the specified
$ssl connection. This is a non-blocking function like L<Net::SSLeay::write()>.

 my $rv = Net::SSLeay::write_partial($ssl, $from, $count, $data);
 # $ssl - value corresponding to openssl's SSL structure
 # $from - (integer) offset from the beginning of $data
 # $count - (integer) length of data to be written
 # $data - data buffer
 #
 # returns: >0 - (success) number of bytes actually written to the TLS/SSL connection
 #           0 - write not successful, probably the underlying connection was closed
 #          <0 - error

=item * set_tlsext_host_name

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before; requires at least openssl-0.9.8f

Sets TLS servername extension on SLL object $ssl to value $name.

 my $rv = set_tlsext_host_name($ssl, $name);
 # $ssl - value corresponding to openssl's SSL structure
 # $name - (string) name to be set
 #
 # returns: 1 on success, 0 on failure

=back

=head3 Low level API: RAND_* related functions

Check openssl doc related to RAND stuff L<http://www.openssl.org/docs/crypto/rand.html|http://www.openssl.org/docs/crypto/rand.html>

=over

=item * RAND_add

Mixes the $num bytes at $buf into the PRNG state.

 Net::SSLeay::RAND_add($buf, $num, $entropy);
 # $buf - buffer with data to be mixed into the PRNG state
 # $num - number of bytes in $buf
 # $entropy - estimate of how much randomness is contained in $buf (in bytes)
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/crypto/RAND_add.html|http://www.openssl.org/docs/crypto/RAND_add.html>

=item * RAND_seed

Equivalent to L</RAND_add> when $num == $entropy.

 Net::SSLeay::RAND_seed($buf);   # Perlishly figures out buf size
 # $buf - buffer with data to be mixed into the PRNG state
 # $num - number of bytes in $buf
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/crypto/RAND_add.html|http://www.openssl.org/docs/crypto/RAND_add.html>

=item * RAND_status

Gives PRNG status (seeded enough or not).

 my $rv = Net::SSLeay::RAND_status();
 #returns: 1 if the PRNG has been seeded with enough data, 0 otherwise

Check openssl doc L<http://www.openssl.org/docs/crypto/RAND_add.html|http://www.openssl.org/docs/crypto/RAND_add.html>

=item * RAND_bytes

Puts $num cryptographically strong pseudo-random bytes into $buf.

 my $rv = Net::SSLeay::RAND_bytes($buf, $num);
 # $buf - buffer where the random data will be stored
 # $num - the size (in bytes) of requested random data
 #
 # returns: 1 on success, -1 if not supported by the current RAND method, or 0 on other failure

Check openssl doc L<http://www.openssl.org/docs/manmaster/man3/RAND_bytes.html|http://www.openssl.org/docs/manmaster/man3/RAND_bytes.html>

=item * RAND_priv_bytes

B<COMPATIBILITY:> not available in Net-SSLeay-1.85 and before; requires at least OpenSSL 1.1.1, not in LibreSSL

Puts $num cryptographically strong pseudo-random bytes into $buf.

 my $rv = Net::SSLeay::RAND_priv_bytes($buf, $num);
 # $buf - buffer where the random data will be stored
 # $num - the size (in bytes) of requested random data
 #
 # returns: 1 on success, -1 if not supported by the current RAND method, or 0 on other failure

RAND_priv_bytes has the same semantics as RAND_bytes, but see see the documentation for more information.

Check openssl doc L<http://www.openssl.org/docs/manmaster/man3/RAND_priv_bytes.html|http://www.openssl.org/docs/manmaster/man3/RAND_priv_bytes.html>

=item * RAND_pseudo_bytes

Puts $num pseudo-random (not necessarily unpredictable) bytes into $buf.

 my $rv = Net::SSLeay::RAND_pseudo_bytes($buf, $num);
 # $buf - buffer where the random data will be stored
 # $num - the size (in bytes) of requested random data
 #
 # returns: 1 if the bytes generated are cryptographically strong, 0 otherwise

Check openssl doc L<http://www.openssl.org/docs/crypto/RAND_bytes.html|http://www.openssl.org/docs/crypto/RAND_bytes.html>

=item * RAND_cleanup

Erase the PRNG state.

 Net::SSLeay::RAND_cleanup();
 # no args, no return value

Check openssl doc L<http://www.openssl.org/docs/crypto/RAND_cleanup.html|http://www.openssl.org/docs/crypto/RAND_cleanup.html>

=item * RAND_egd_bytes

Queries the entropy gathering daemon EGD on socket $path for $bytes bytes.

 my $rv = Net::SSLeay::RAND_egd_bytes($path, $bytes);
 # $path - path to a socket of entropy gathering daemon EGD
 # $bytes - number of bytes we want from EGD
 #
 # returns: the number of bytes read from the daemon on success, and -1 on failure

Check openssl doc L<http://www.openssl.org/docs/crypto/RAND_egd.html|http://www.openssl.org/docs/crypto/RAND_egd.html>

=item * RAND_file_name

Generates a default path for the random seed file.

 my $file = Net::SSLeay::RAND_file_name($num);
 # $num - maximum size of returned file name
 #
 # returns: string with file name on success, '' (empty string) on failure

Check openssl doc L<http://www.openssl.org/docs/crypto/RAND_load_file.html|http://www.openssl.org/docs/crypto/RAND_load_file.html>

=item * RAND_load_file

B<COMPATIBILITY:> Is no longer functional on LibreSSL

Reads $max_bytes of bytes from $file_name and adds them to the PRNG.

 my $rv = Net::SSLeay::RAND_load_file($file_name, $max_bytes);
 # $file_name - the name of file
 # $max_bytes - bytes to read from $file_name; -1 => the complete file is read
 #
 # returns: the number of bytes read

Check openssl doc L<http://www.openssl.org/docs/crypto/RAND_load_file.html|http://www.openssl.org/docs/crypto/RAND_load_file.html>

=item * RAND_write_file

Writes 1024 random bytes to $file_name which can be used to initialize the PRNG by calling L</RAND_load_file> in a later session.

 my $rv = Net::SSLeay::RAND_write_file($file_name);
 # $file_name - the name of file
 #
 # returns: the number of bytes written, and -1 if the bytes written were generated without appropriate seed

Check openssl doc L<http://www.openssl.org/docs/crypto/RAND_load_file.html|http://www.openssl.org/docs/crypto/RAND_load_file.html>

=item * RAND_poll

Collects some entropy from operating system and adds it to the PRNG.

 my $rv = Net::SSLeay::RAND_poll();
 # returns: 1 on success, 0 on failure (unable to gather reasonable entropy)

=back

=head3 Low level API: OBJ_* related functions

=over

=item * OBJ_cmp

Compares ASN1_OBJECT $a to ASN1_OBJECT $b.

 my $rv = Net::SSLeay::OBJ_cmp($a, $b);
 # $a - value corresponding to openssl's ASN1_OBJECT structure
 # $b - value corresponding to openssl's ASN1_OBJECT structure
 #
 # returns: if the two are identical 0 is returned

Check openssl doc L<http://www.openssl.org/docs/crypto/OBJ_nid2obj.html|http://www.openssl.org/docs/crypto/OBJ_nid2obj.html>

=item * OBJ_dup

Returns a copy/duplicate of $o.

 my $rv = Net::SSLeay::OBJ_dup($o);
 # $o - value corresponding to openssl's ASN1_OBJECT structure
 #
 # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/crypto/OBJ_nid2obj.html|http://www.openssl.org/docs/crypto/OBJ_nid2obj.html>

=item * OBJ_nid2ln

Returns long name for given NID $n.

 my $rv = Net::SSLeay::OBJ_nid2ln($n);
 # $n - (integer) NID
 #
 # returns: (string) long name e.g. 'commonName'

Check openssl doc L<http://www.openssl.org/docs/crypto/OBJ_nid2obj.html|http://www.openssl.org/docs/crypto/OBJ_nid2obj.html>

=item * OBJ_ln2nid

Returns NID corresponding to given long name $n.

 my $rv = Net::SSLeay::OBJ_ln2nid($s);
 # $s - (string) long name e.g. 'commonName'
 #
 # returns: (integer) NID

=item * OBJ_nid2sn

Returns short name for given NID $n.

 my $rv = Net::SSLeay::OBJ_nid2sn($n);
 # $n - (integer) NID
 #
 # returns: (string) short name e.g. 'CN'

Example:

 print Net::SSLeay::OBJ_nid2sn(&Net::SSLeay::NID_commonName);

=item * OBJ_sn2nid

Returns NID corresponding to given short name $s.

 my $rv = Net::SSLeay::OBJ_sn2nid($s);
 # $s - (string) short name e.g. 'CN'
 #
 # returns: (integer) NID

Example:

 print "NID_commonName constant=", &Net::SSLeay::NID_commonName;
 print "OBJ_sn2nid('CN')=", Net::SSLeay::OBJ_sn2nid('CN');

=item * OBJ_nid2obj

Returns ASN1_OBJECT for given NID $n.

 my $rv = Net::SSLeay::OBJ_nid2obj($n);
 # $n - (integer) NID
 #
 # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/crypto/OBJ_nid2obj.html|http://www.openssl.org/docs/crypto/OBJ_nid2obj.html>

=item * OBJ_obj2nid

Returns NID corresponding to given ASN1_OBJECT $o.

 my $rv = Net::SSLeay::OBJ_obj2nid($o);
 # $o - value corresponding to openssl's ASN1_OBJECT structure
 #
 # returns: (integer) NID

Check openssl doc L<http://www.openssl.org/docs/crypto/OBJ_nid2obj.html|http://www.openssl.org/docs/crypto/OBJ_nid2obj.html>

=item * OBJ_txt2obj

Converts the text string s into an ASN1_OBJECT structure. If $no_name is 0 then
long names (e.g. 'commonName') and short names (e.g. 'CN') will be interpreted
as well as numerical forms (e.g. '2.5.4.3'). If $no_name is 1 only the numerical
form is acceptable.

 my $rv = Net::SSLeay::OBJ_txt2obj($s, $no_name);
 # $s - text string to be converted
 # $no_name - (integer) 0 or 1
 #
 # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/crypto/OBJ_nid2obj.html|http://www.openssl.org/docs/crypto/OBJ_nid2obj.html>

=item * OBJ_obj2txt

Converts the ASN1_OBJECT a into a textual representation.

 Net::SSLeay::OBJ_obj2txt($a, $no_name);
 # $a - value corresponding to openssl's ASN1_OBJECT structure
 # $no_name - (integer) 0 or 1
 #
 # returns: textual representation e.g. 'commonName' ($no_name=0), '2.5.4.3' ($no_name=1)

Check openssl doc L<http://www.openssl.org/docs/crypto/OBJ_nid2obj.html|http://www.openssl.org/docs/crypto/OBJ_nid2obj.html>

=item * OBJ_txt2nid

Returns NID corresponding to text string $s which can be a long name, a short name or the numerical representation of an object.

 my $rv = Net::SSLeay::OBJ_txt2nid($s);
 # $s - (string) e.g. 'commonName' or 'CN' or '2.5.4.3'
 #
 # returns: (integer) NID

Example:

 my $nid = Net::SSLeay::OBJ_txt2nid('2.5.4.3');
 Net::SSLeay::OBJ_nid2sn($n);

Check openssl doc L<http://www.openssl.org/docs/crypto/OBJ_nid2obj.html|http://www.openssl.org/docs/crypto/OBJ_nid2obj.html>

=back

=head3 Low level API: ASN1_INTEGER_* related functions

=over

=item * ASN1_INTEGER_new

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Creates a new ASN1_INTEGER structure.

 my $rv = Net::SSLeay::ASN1_INTEGER_new();
 #
 # returns: value corresponding to openssl's ASN1_INTEGER structure (0 on failure)

=item * ASN1_INTEGER_free

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Free an allocated ASN1_INTEGER structure.

 Net::SSLeay::ASN1_INTEGER_free($i);
 # $i - value corresponding to openssl's ASN1_INTEGER structure
 #
 # returns: no return value

=item * ASN1_INTEGER_get

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns integer value of given ASN1_INTEGER object.

B<BEWARE:> If the value stored in ASN1_INTEGER is greater than max. integer that can be stored
in 'long' type (usually 32bit but may vary according to platform) then this function will return -1.
For getting large ASN1_INTEGER values consider using L</P_ASN1_INTEGER_get_dec> or L</P_ASN1_INTEGER_get_hex>.

 my $rv = Net::SSLeay::ASN1_INTEGER_get($a);
 # $a - value corresponding to openssl's ASN1_INTEGER structure
 #
 # returns: integer value of ASN1_INTEGER object in $a

=item * ASN1_INTEGER_set

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Sets value of given ASN1_INTEGER object to value $val

B<BEWARE:> $val has max. limit (= max. integer that can be stored in 'long' type).
For setting large ASN1_INTEGER values consider using L</P_ASN1_INTEGER_set_dec> or L</P_ASN1_INTEGER_set_hex>.

 my $rv = Net::SSLeay::ASN1_INTEGER_set($i, $val);
 # $i - value corresponding to openssl's ASN1_INTEGER structure
 # $val - integer value
 #
 # returns: 1 on success, 0 on failure

=item * P_ASN1_INTEGER_get_dec

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns string with decimal representation of integer value of given ASN1_INTEGER object.

 Net::SSLeay::P_ASN1_INTEGER_get_dec($i);
 # $i - value corresponding to openssl's ASN1_INTEGER structure
 #
 # returns: string with decimal representation

=item * P_ASN1_INTEGER_get_hex

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns string with hexadecimal representation of integer value of given ASN1_INTEGER object.

 Net::SSLeay::P_ASN1_INTEGER_get_hex($i);
 # $i - value corresponding to openssl's ASN1_INTEGER structure
 #
 # returns: string with hexadecimal representation

=item * P_ASN1_INTEGER_set_dec

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Sets value of given ASN1_INTEGER object to value $val (decimal string, suitable for large integers)

 Net::SSLeay::P_ASN1_INTEGER_set_dec($i, $str);
 # $i - value corresponding to openssl's ASN1_INTEGER structure
 # $str - string with decimal representation
 #
 # returns: 1 on success, 0 on failure

=item * P_ASN1_INTEGER_set_hex

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Sets value of given ASN1_INTEGER object to value $val (hexadecimal string, suitable for large integers)

 Net::SSLeay::P_ASN1_INTEGER_set_hex($i, $str);
 # $i - value corresponding to openssl's ASN1_INTEGER structure
 # $str - string with hexadecimal representation
 #
 # returns: 1 on success, 0 on failure

=back

=head3 Low level API: ASN1_STRING_* related functions

=over

=item * P_ASN1_STRING_get

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns string value of given ASN1_STRING object.

 Net::SSLeay::P_ASN1_STRING_get($s, $utf8_decode);
 # $s - value corresponding to openssl's ASN1_STRING structure
 # $utf8_decode - [optional] 0 or 1 whether the returned value should be utf8 decoded (default=0)
 #
 # returns: string

 $string = Net::SSLeay::P_ASN1_STRING_get($s);
 #is the same as:
 $string = Net::SSLeay::P_ASN1_STRING_get($s, 0);

=back

=head3 Low level API: ASN1_TIME_* related functions

=over

=item * ASN1_TIME_new

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before

 my $time = ASN1_TIME_new();
 # returns: value corresponding to openssl's ASN1_TIME structure

=item * ASN1_TIME_free

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before

 ASN1_TIME_free($time);
 # $time - value corresponding to openssl's ASN1_TIME structure

=item * ASN1_TIME_set

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before

 ASN1_TIME_set($time, $t);
 # $time - value corresponding to openssl's ASN1_TIME structure
 # $t - time value in seconds since 1.1.1970

B<BEWARE:> It is platform dependent how this function will handle dates after 2038.
Although perl's integer is large enough the internal implementation of this function
is dependent on the size of time_t structure (32bit time_t has problem with 2038).

If you want to safely set date and time after 2038 use function L</P_ASN1_TIME_set_isotime>.

=item * P_ASN1_TIME_get_isotime

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before; requires at least openssl-0.9.7e

B<NOTE:> Does not exactly correspond to any low level API function

Gives ISO-8601 string representation of ASN1_TIME structure.

 my $datetime_string = P_ASN1_TIME_get_isotime($time);
 # $time - value corresponding to openssl's ASN1_TIME structure
 #
 # returns: datetime string like '2033-05-16T20:39:37Z' or '' on failure

The output format is compatible with module L<DateTime::Format::RFC3339>

=item * P_ASN1_TIME_set_isotime

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before; requires at least openssl-0.9.7e

B<NOTE:> Does not exactly correspond to any low level API function

Sets time and date value of ANS1_time structure.

 my $rv = P_ASN1_TIME_set_isotime($time, $string);
 # $time - value corresponding to openssl's ASN1_TIME structure
 # $string - ISO-8601 timedate string like '2033-05-16T20:39:37Z'
 #
 # returns: 1 on success, 0 on failure

The C<$string> parameter has to be in full form like C<"2012-03-22T23:55:33"> or
C<"2012-03-22T23:55:33Z"> or C<"2012-03-22T23:55:33CET">. Short forms like
C<"2012-03-22T23:55"> or C<"2012-03-22"> are not supported.

=item * P_ASN1_TIME_put2string

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before, has bugs with openssl-0.9.8i

B<NOTE:> Does not exactly correspond to any low level API function

Gives string representation of ASN1_TIME structure.

 my $str = P_ASN1_TIME_put2string($time);
 # $time - value corresponding to openssl's ASN1_TIME structure
 #
 # returns: datetime string like 'May 16 20:39:37 2033 GMT'

=item * P_ASN1_UTCTIME_put2string

B<NOTE:> deprecated function, only for backward compatibility, just an alias
for L</P_ASN1_TIME_put2string>

=back

=head3 Low level API: X509_* related functions

=over

=item * X509_new

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Allocates and initializes a X509 structure.

 my $rv = Net::SSLeay::X509_new();
 #
 # returns: value corresponding to openssl's X509 structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_new.html|http://www.openssl.org/docs/crypto/X509_new.html>

=item * X509_free

Frees up the X509 structure.

 Net::SSLeay::X509_free($a);
 # $a - value corresponding to openssl's X509 structure
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_new.html|http://www.openssl.org/docs/crypto/X509_new.html>

=item * X509_check_host

B<COMPATIBILITY:> not available in Net-SSLeay-1.68 and before; requires at
least OpenSSL 1.0.2. X509_CHECK_FLAG_NEVER_CHECK_SUBJECT requires OpenSSL 1.1.0.

Checks f the certificate Subject Alternative Name (SAN) or Subject CommonName
(CN) matches the specified host name.

 my $rv = Net::SSLeay::X509_check_host($cert, $name, $flags, $peername);
 # $cert - value corresponding to openssl's X509 structure
 # $name - host name to check
 # $flags (optional, default: 0) - can be the bitwise OR of:
 #   &Net::SSLeay::X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT
 #   &Net::SSLeay::X509_CHECK_FLAG_NO_WILDCARDS
 #   &Net::SSLeay::X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS
 #   &Net::SSLeay::X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS
 #   &Net::SSLeay::X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS
 #   &Net::SSLeay::X509_CHECK_FLAG_NEVER_CHECK_SUBJECT
 # $peername (optional) - If not omitted and $host matches $cert,
 #                        a copy of the matching SAN or CN from
 #                        the peer certificate is stored in $peername.
 #
 # returns:
 #   1 for a successful match
 #   0 for a failed match
 #  -1 for an internal error
 #  -2 if the input is malformed

Check openssl doc L<https://www.openssl.org/docs/crypto/X509_check_host.html>.

=item * X509_check_email

B<COMPATIBILITY:> not available in Net-SSLeay-1.68 and before; requires at least OpenSSL 1.0.2.

Checks if the certificate matches the specified email address.

 my $rv = Net::SSLeay::X509_check_email($cert, $address, $flags);
 # $cert - value corresponding to openssl's X509 structure
 # $address - email address to check
 # $flags (optional, default: 0) - see X509_check_host()
 #
 # returns: see X509_check_host()

Check openssl doc L<https://www.openssl.org/docs/crypto/X509_check_email.html>.

=item * X509_check_ip

B<COMPATIBILITY:> not available in Net-SSLeay-1.68 and before; requires at least OpenSSL 1.0.2.

Checks if the certificate matches the specified IPv4 or IPv6 address.

 my $rv = Net::SSLeay::X509_check_email($cert, $address, $flags);
 # $cert - value corresponding to openssl's X509 structure
 # $address - IP address to check in binary format, in network byte order
 # $flags (optional, default: 0) - see X509_check_host()
 #
 # returns: see X509_check_host()

Check openssl doc L<https://www.openssl.org/docs/crypto/X509_check_ip.html>.

=item * X509_check_ip_asc

B<COMPATIBILITY:> not available in Net-SSLeay-1.68 and before; requires at least OpenSSL 1.0.2.

Checks if the certificate matches the specified IPv4 or IPv6 address.

 my $rv = Net::SSLeay::X509_check_email($cert, $address, $flags);
 # $cert - value corresponding to openssl's X509 structure
 # $address - IP address to check in text representation
 # $flags (optional, default: 0) - see X509_check_host()
 #
 # returns: see X509_check_host()

Check openssl doc L<https://www.openssl.org/docs/crypto/X509_check_ip_asc.html>.

=item * X509_certificate_type

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns bitmask with type of certificate $x.

 my $rv = Net::SSLeay::X509_certificate_type($x);
 # $x - value corresponding to openssl's X509 structure
 #
 # returns: (integer) bitmask with certificate type

 #to decode bitmask returned by this function use these constants:
 &Net::SSLeay::EVP_PKS_DSA
 &Net::SSLeay::EVP_PKS_EC
 &Net::SSLeay::EVP_PKS_RSA
 &Net::SSLeay::EVP_PKT_ENC
 &Net::SSLeay::EVP_PKT_EXCH
 &Net::SSLeay::EVP_PKT_EXP
 &Net::SSLeay::EVP_PKT_SIGN
 &Net::SSLeay::EVP_PK_DH
 &Net::SSLeay::EVP_PK_DSA
 &Net::SSLeay::EVP_PK_EC
 &Net::SSLeay::EVP_PK_RSA

=item * X509_digest

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Computes digest/fingerprint of X509 $data using $type hash function.

 my $digest_value = Net::SSLeay::X509_digest($data, $type);
 # $data - value corresponding to openssl's X509 structure
 # $type - value corresponding to openssl's EVP_MD structure - e.g. got via EVP_get_digestbyname()
 #
 # returns: hash value (binary)

 #to get printable (hex) value of digest use:
 print unpack('H*', $digest_value);

=item * X509_issuer_and_serial_hash

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Sort of a checksum of issuer name and serial number of X509 certificate $x.
The result is not a full hash (e.g. sha-1), it is kind-of-a-hash truncated to the size of 'unsigned long' (32 bits).
The resulting value might differ across different openssl versions for the same X509 certificate.

 my $rv = Net::SSLeay::X509_issuer_and_serial_hash($x);
 # $x - value corresponding to openssl's X509 structure
 #
 # returns: number representing checksum

=item * X509_issuer_name_hash

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Sort of a checksum of issuer name of X509 certificate $x.
The result is not a full hash (e.g. sha-1), it is kind-of-a-hash truncated to the size of 'unsigned long' (32 bits).
The resulting value might differ across different openssl versions for the same X509 certificate.

 my $rv = Net::SSLeay::X509_issuer_name_hash($x);
 # $x - value corresponding to openssl's X509 structure
 #
 # returns: number representing checksum

=item * X509_subject_name_hash

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Sort of a checksum of subject name of X509 certificate $x.
The result is not a full hash (e.g. sha-1), it is kind-of-a-hash truncated to the size of 'unsigned long' (32 bits).
The resulting value might differ across different openssl versions for the same X509 certificate.

 my $rv = Net::SSLeay::X509_subject_name_hash($x);
 # $x - value corresponding to openssl's X509 structure
 #
 # returns: number representing checksum

=item * X509_pubkey_digest

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before; requires at least openssl-0.9.7

Computes digest/fingerprint of public key from X509 certificate $data using $type hash function.

 my $digest_value = Net::SSLeay::X509_pubkey_digest($data, $type);
 # $data - value corresponding to openssl's X509 structure
 # $type - value corresponding to openssl's EVP_MD structure - e.g. got via EVP_get_digestbyname()
 #
 # returns: hash value (binary)

 #to get printable (hex) value of digest use:
 print unpack('H*', $digest_value);

=item * X509_set_issuer_name

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Sets issuer of X509 certificate $x to $name.

 my $rv = Net::SSLeay::X509_set_issuer_name($x, $name);
 # $x - value corresponding to openssl's X509 structure
 # $name - value corresponding to openssl's X509_NAME structure
 #
 # returns: 1 on success, 0 on failure

=item * X509_set_pubkey

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Sets public key of X509 certificate $x to $pkey.

 my $rv = Net::SSLeay::X509_set_pubkey($x, $pkey);
 # $x - value corresponding to openssl's X509 structure
 # $pkey - value corresponding to openssl's EVP_PKEY structure
 #
 # returns: 1 on success, 0 on failure

=item * X509_set_serialNumber

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Sets serial number of X509 certificate $x to $serial.

 my $rv = Net::SSLeay::X509_set_serialNumber($x, $serial);
 # $x - value corresponding to openssl's X509 structure
 # $serial - value corresponding to openssl's ASN1_INTEGER structure
 #
 # returns: 1 on success, 0 on failure

 #to create $serial value use one of these:
 $serial = Net::SSLeay::P_ASN1_INTEGER_set_hex('45ad6f');
 $serial = Net::SSLeay::P_ASN1_INTEGER_set_dec('7896541238529631478');
 $serial = Net::SSLeay::ASN1_INTEGER_set(45896);

=item * X509_set_subject_name

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Sets subject of X509 certificate $x to $name.

 my $rv = Net::SSLeay::X509_set_subject_name($x, $name);
 # $x - value corresponding to openssl's X509 structure
 # $name - value corresponding to openssl's X509_NAME structure
 #
 # returns: 1 on success, 0 on failure

=item * X509_set_version

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Set 'version' value for X509 certificate $ to $version.

 my $rv = Net::SSLeay::X509_set_version($x, $version);
 # $x - value corresponding to openssl's X509 structure
 # $version - (integer) version number
 #
 # returns: 1 on success, 0 on failure

=item * X509_sign

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Sign X509 certificate $x with private key $pkey (using digest algorithm $md).

 my $rv = Net::SSLeay::X509_sign($x, $pkey, $md);
 # $x - value corresponding to openssl's X509 structure
 # $pkey - value corresponding to openssl's EVP_PKEY structure
 # $md - value corresponding to openssl's EVP_MD structure
 #
 # returns: 1 on success, 0 on failure

=item * X509_verify

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Verifies X509 object $a using public key $r (pubkey of issuing CA).

 my $rv = Net::SSLeay::X509_verify($x, $r);
 # $x - value corresponding to openssl's X509 structure
 # $r - value corresponding to openssl's EVP_PKEY structure
 #
 # returns: 0 - verify failure, 1 - verify OK, <0 - error

=item * X509_get_ext_count

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns the total number of extensions in X509 object $x.

 my $rv = Net::SSLeay::X509_get_ext_count($x);
 # $x - value corresponding to openssl's X509 structure
 #
 # returns: count of extensions

=item * X509_get_pubkey

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns public key corresponding to given X509 object $x.

 my $rv = Net::SSLeay::X509_get_pubkey($x);
 # $x - value corresponding to openssl's X509 structure
 #
 # returns: value corresponding to openssl's EVP_PKEY structure (0 on failure)

B<NOTE:> This method returns only the public key's key bits, without the
algorithm or parameters.  Use C<X509_get_X509_PUBKEY()> to return the full
public key (SPKI) instead.

=item * X509_get_X509_PUBKEY

B<COMPATIBILITY:> not available in Net-SSLeay-1.72 and before

Returns the full public key (SPKI) of given X509 certificate $x.

 Net::SSLeay::X509_get_X509_PUBKEY($x);
 # $x - value corresponding to openssl's X509 structure
 #
 # returns: public key data in DER format (binary)

=item * X509_get_serialNumber

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns serial number of X509 certificate $x.

 my $rv = Net::SSLeay::X509_get_serialNumber($x);
 # $x - value corresponding to openssl's X509 structure
 #
 # returns: value corresponding to openssl's ASN1_INTEGER structure (0 on failure)

See L</P_ASN1_INTEGER_get_dec>, L</P_ASN1_INTEGER_get_hex> or L</ASN1_INTEGER_get> to decode ASN1_INTEGER object.

=item * X509_get0_serialNumber

B<COMPATIBILITY:> available in Net-SSLeay-1.86 onwards

X509_get0_serialNumber() is the same as X509_get_serialNumber() except it accepts a const parameter and returns a const result.

=item * X509_get_version

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns 'version' value of given X509 certificate $x.

 my $rv = Net::SSLeay::X509_get_version($x);
 # $x - value corresponding to openssl's X509 structure
 #
 # returns: (integer) version

=item * X509_get_ext

Returns X509_EXTENSION from $x509 based on given position/index.

 my $rv = Net::SSLeay::X509_get_ext($x509, $index);
 # $x509 - value corresponding to openssl's X509 structure
 # $index - (integer) position/index of extension within $x509
 #
 # returns: value corresponding to openssl's X509_EXTENSION structure (0 on failure)

=item * X509_get_ext_by_NID

Returns X509_EXTENSION from $x509 based on given NID.

 my $rv = Net::SSLeay::X509_get_ext_by_NID($x509, $nid, $loc);
 # $x509 - value corresponding to openssl's X509 structure
 # $nid - (integer) NID value
 # $loc - (integer) position to start lookup at
 #
 # returns: position/index of extension, negative value on error
 #          call Net::SSLeay::X509_get_ext($x509, $rv) to get the actual extension

=item * X509_get_fingerprint

Returns fingerprint of certificate $cert.

B<NOTE:> Does not exactly correspond to any low level API function. The implementation
is basen on openssl's C<X509_digest()>.

 Net::SSLeay::X509_get_fingerprint($x509, $type);
 # $x509 - value corresponding to openssl's X509 structure
 # $type - (string) digest type, currently supported values:
 #         "md5"
 #         "sha1"
 #         "sha256"
 #         "ripemd160"
 #
 # returns: certificate digest - hexadecimal string (NOT binary data!)

=item * X509_get_issuer_name

Return an X509_NAME object representing the issuer of the certificate $cert.

 my $rv = Net::SSLeay::X509_get_issuer_name($cert);
 # $cert - value corresponding to openssl's X509 structure
 #
 # returns: value corresponding to openssl's X509_NAME structure (0 on failure)

=item * X509_get_notAfter

Return an object giving the time after which the certificate $cert is not valid.

 my $rv = Net::SSLeay::X509_get_notAfter($cert);
 # $cert - value corresponding to openssl's X509 structure
 #
 # returns: value corresponding to openssl's ASN1_TIME structure (0 on failure)

To get human readable/printable form the return value you can use:

 my $time = Net::SSLeay::X509_get_notAfter($cert);
 print "notAfter=", Net::SSLeay::P_ASN1_TIME_get_isotime($time), "\n";

=item * X509_get_notBefore

Return an object giving the time before which the certificate $cert is not valid

 my $rv = Net::SSLeay::X509_get_notBefore($cert);
 # $cert - value corresponding to openssl's X509 structure
 #
 # returns: value corresponding to openssl's ASN1_TIME structure (0 on failure)

To get human readable/printable form the return value you can use:

 my $time = Net::SSLeay::X509_get_notBefore($cert);
 print "notBefore=", Net::SSLeay::P_ASN1_TIME_get_isotime($time), "\n";

=item * X509_get_subjectAltNames

B<NOTE:> Does not exactly correspond to any low level API function.

Returns the list of alternative subject names from X509 certificate $cert.

 my @rv = Net::SSLeay::X509_get_subjectAltNames($cert);
 # $cert - value corresponding to openssl's X509 structure
 #
 # returns: list containing pairs - name_type (integer), name_value (string)
 #          where name_type can be:
 #          0 - GEN_OTHERNAME
 #          1 - GEN_EMAIL
 #          2 - GEN_DNS
 #          3 - GEN_X400
 #          4 - GEN_DIRNAME
 #          5 - GEN_EDIPARTY
 #          6 - GEN_URI
 #          7 - GEN_IPADD
 #          8 - GEN_RID

Note: type 7 - GEN_IPADD contains the IP address as a packed binary address.

=item * X509_get_subject_name

Returns the subject of the certificate $cert.

 my $rv = Net::SSLeay::X509_get_subject_name($cert);
 # $cert - value corresponding to openssl's X509 structure
 #
 # returns: value corresponding to openssl's X509_NAME structure (0 on failure)

=item * X509_gmtime_adj

Adjust th ASN1_TIME object to the timestamp (in GMT).

 my $rv = Net::SSLeay::X509_gmtime_adj($s, $adj);
 # $s - value corresponding to openssl's ASN1_TIME structure
 # $adj - timestamp (seconds since 1.1.1970)
 #
 # returns: value corresponding to openssl's ASN1_TIME structure (0 on failure)

B<BEWARE:> this function may fail for dates after 2038 as it is dependent on time_t size on your
system (32bit time_t does not work after 2038). Consider using L</P_ASN1_TIME_set_isotime> instead).

=item * X509_load_cert_crl_file

Takes PEM file and loads all X509 certificates and X509 CRLs from that file into X509_LOOKUP structure.

 my $rv = Net::SSLeay::X509_load_cert_crl_file($ctx, $file, $type);
 # $ctx - value corresponding to openssl's X509_LOOKUP structure
 # $file - (string) file name
 # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
 #                          if not FILETYPE_PEM then behaves as Net::SSLeay::X509_load_cert_file()
 #
 # returns: 1 on success, 0 on failure

=item * X509_load_cert_file

Loads/adds X509 certificate from $file to X509_LOOKUP structure

 my $rv = Net::SSLeay::X509_load_cert_file($ctx, $file, $type);
 # $ctx - value corresponding to openssl's X509_LOOKUP structure
 # $file - (string) file name
 # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
 #
 # returns: 1 on success, 0 on failure

=item * X509_load_crl_file

Loads/adds X509 CRL from $file to X509_LOOKUP structure

 my $rv = Net::SSLeay::X509_load_crl_file($ctx, $file, $type);
 # $ctx - value corresponding to openssl's X509_LOOKUP structure
 # $file - (string) file name
 # $type - (integer) type - use constants &Net::SSLeay::FILETYPE_PEM or &Net::SSLeay::FILETYPE_ASN1
 #
 # returns: 1 on success, 0 on failure

=item * X509_policy_level_get0_node

??? (more info needed)

 my $rv = Net::SSLeay::X509_policy_level_get0_node($level, $i);
 # $level - value corresponding to openssl's X509_POLICY_LEVEL structure
 # $i - (integer) index/position
 #
 # returns: value corresponding to openssl's X509_POLICY_NODE structure (0 on failure)

=item * X509_policy_level_node_count

??? (more info needed)

 my $rv = Net::SSLeay::X509_policy_level_node_count($level);
 # $level - value corresponding to openssl's X509_POLICY_LEVEL structure
 #
 # returns: (integer) node count

=item * X509_policy_node_get0_parent

??? (more info needed)

 my $rv = Net::SSLeay::X509_policy_node_get0_parent($node);
 # $node - value corresponding to openssl's X509_POLICY_NODE structure
 #
 # returns: value corresponding to openssl's X509_POLICY_NODE structure (0 on failure)

=item * X509_policy_node_get0_policy

??? (more info needed)

 my $rv = Net::SSLeay::X509_policy_node_get0_policy($node);
 # $node - value corresponding to openssl's X509_POLICY_NODE structure
 #
 # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

=item * X509_policy_node_get0_qualifiers

??? (more info needed)

 my $rv = Net::SSLeay::X509_policy_node_get0_qualifiers($node);
 # $node - value corresponding to openssl's X509_POLICY_NODE structure
 #
 # returns: value corresponding to openssl's STACK_OF(POLICYQUALINFO) structure (0 on failure)

=item * X509_policy_tree_free

??? (more info needed)

 Net::SSLeay::X509_policy_tree_free($tree);
 # $tree - value corresponding to openssl's X509_POLICY_TREE structure
 #
 # returns: no return value

=item * X509_policy_tree_get0_level

??? (more info needed)

 my $rv = Net::SSLeay::X509_policy_tree_get0_level($tree, $i);
 # $tree - value corresponding to openssl's X509_POLICY_TREE structure
 # $i - (integer) level index
 #
 # returns: value corresponding to openssl's X509_POLICY_LEVEL structure (0 on failure)

=item * X509_policy_tree_get0_policies

??? (more info needed)

 my $rv = Net::SSLeay::X509_policy_tree_get0_policies($tree);
 # $tree - value corresponding to openssl's X509_POLICY_TREE structure
 #
 # returns: value corresponding to openssl's X509_POLICY_NODE structure (0 on failure)

=item * X509_policy_tree_get0_user_policies

??? (more info needed)

 my $rv = Net::SSLeay::X509_policy_tree_get0_user_policies($tree);
 # $tree - value corresponding to openssl's X509_POLICY_TREE structure
 #
 # returns: value corresponding to openssl's X509_POLICY_NODE structure (0 on failure)

=item * X509_policy_tree_level_count

??? (more info needed)

 my $rv = Net::SSLeay::X509_policy_tree_level_count($tree);
 # $tree - value corresponding to openssl's X509_POLICY_TREE structure
 #
 # returns: (integer) count

=item * X509_verify_cert_error_string

Returns a human readable error string for verification error $n.

 my $rv = Net::SSLeay::X509_verify_cert_error_string($n);
 # $n - (long) numeric error code
 #
 # returns: error string

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_STORE_CTX_get_error.html|http://www.openssl.org/docs/crypto/X509_STORE_CTX_get_error.html>

=item * P_X509_add_extensions

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Adds one or more X509 extensions to X509 object $x.

 my $rv = Net::SSLeay::P_X509_add_extensions($x, $ca_cert, $nid, $value);
 # $x - value corresponding to openssl's X509 structure
 # $ca_cert - value corresponding to openssl's X509 structure (issuer's cert - necessary for sertting NID_authority_key_identifier)
 # $nid - NID identifying extension to be set
 # $value - extension value
 #
 # returns: 1 on success, 0 on failure

You can set more extensions at once:

 my $rv = Net::SSLeay::P_X509_add_extensions($x509, $ca_cert,
                &Net::SSLeay::NID_key_usage => 'digitalSignature,keyEncipherment',
                &Net::SSLeay::NID_subject_key_identifier => 'hash',
                &Net::SSLeay::NID_authority_key_identifier => 'keyid',
                &Net::SSLeay::NID_authority_key_identifier => 'issuer',
                &Net::SSLeay::NID_basic_constraints => 'CA:FALSE',
                &Net::SSLeay::NID_ext_key_usage => 'serverAuth,clientAuth',
                &Net::SSLeay::NID_netscape_cert_type => 'server',
                &Net::SSLeay::NID_subject_alt_name => 'DNS:s1.dom.com,DNS:s2.dom.com,DNS:s3.dom.com',
          );

=item * P_X509_copy_extensions

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Copies X509 extensions from X509_REQ object to X509 object - handy when you need to turn X509_REQ into X509 certificate.

 Net::SSLeay::P_X509_copy_extensions($x509_req, $x509, $override);
 # $x509_req - value corresponding to openssl's X509_REQ structure
 # $x509 - value corresponding to openssl's X509 structure
 # $override - (integer) flag indication whether to override already existing items in $x509 (default 1)
 #
 # returns: 1 on success, 0 on failure

=item * P_X509_get_crl_distribution_points

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before; requires at least openssl-0.9.7

Get the list of CRL distribution points from X509 certificate.

 my @cdp = Net::SSLeay::P_X509_get_crl_distribution_points($x509);
 # $x509 - value corresponding to openssl's X509 structure
 #
 # returns: list of distribution points (usually URLs)

=item * P_X509_get_ext_key_usage

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before; requires at least openssl-0.9.7

Gets the list of extended key usage of given X509 certificate $cert.

 my @ext_usage = Net::SSLeay::P_X509_get_ext_key_usage($cert, $format);
 # $cert - value corresponding to openssl's X509 structure
 # $format - choose type of return values: 0=OIDs, 1=NIDs, 2=shortnames, 3=longnames
 #
 # returns: list of values

Examples:

 my @extkeyusage_oid = Net::SSLeay::P_X509_get_ext_key_usage($x509,0);
 # returns for example: ("1.3.6.1.5.5.7.3.1", "1.3.6.1.5.5.7.3.2")

 my @extkeyusage_nid = Net::SSLeay::P_X509_get_ext_key_usage($x509,1);
 # returns for example: (129, 130)

 my @extkeyusage_sn  = Net::SSLeay::P_X509_get_ext_key_usage($x509,2);
 # returns for example: ("serverAuth", "clientAuth")

 my @extkeyusage_ln  = Net::SSLeay::P_X509_get_ext_key_usage($x509,3);
 # returns for example: ("TLS Web Server Authentication",  "TLS Web Client Authentication")

=item * P_X509_get_key_usage

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Gets the list of key usage of given X509 certificate $cert.

 my @keyusage = Net::SSLeay::P_X509_get_key_usage($cert);
 # $cert - value corresponding to openssl's X509 structure
 #
 # returns: list of key usage values which can be none, one or more from the following list:
 #          "digitalSignature"
 #          "nonRepudiation"
 #          "keyEncipherment"
 #          "dataEncipherment"
 #          "keyAgreement"
 #          "keyCertSign"
 #          "cRLSign"
 #          "encipherOnly"
 #          "decipherOnly"

=item * P_X509_get_netscape_cert_type

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Gets the list of Netscape cert types of given X509 certificate $cert.

 Net::SSLeay::P_X509_get_netscape_cert_type($cert);
 # $cert - value corresponding to openssl's X509 structure
 #
 # returns: list of Netscape type values which can be none, one or more from the following list:
 #          "client"
 #          "server"
 #          "email"
 #          "objsign"
 #          "reserved"
 #          "sslCA"
 #          "emailCA"
 #          "objCA"

=item * P_X509_get_pubkey_alg

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns ASN1_OBJECT corresponding to X509 certificate public key algorithm.

 my $rv = Net::SSLeay::P_X509_get_pubkey_alg($x);
 # $x - value corresponding to openssl's X509 structure
 #
 # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

To get textual representation use:

 my $alg = Net::SSLeay::OBJ_obj2txt(Net::SSLeay::P_X509_get_pubkey_alg($x509));
 # returns for example: "rsaEncryption"

=item * P_X509_get_signature_alg

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns ASN1_OBJECT corresponding to X509 signarite key algorithm.

 my $rv = Net::SSLeay::P_X509_get_signature_alg($x);
 # $x - value corresponding to openssl's X509 structure
 #
 # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

To get textual representation use:

 my $alg = Net::SSLeay::OBJ_obj2txt(Net::SSLeay::P_X509_get_signature_alg($x509))
 # returns for example: "sha1WithRSAEncryption"

=item * sk_X509_new_null

Returns a new, empty, STACK_OF(X509) structure.

 my $rv = Net::SSLeay::sk_X509_new_null();
 #
 # returns: value corresponding to openssl's STACK_OF(X509) structure

=item * sk_X509_push

Pushes an X509 structure onto a STACK_OF(X509) structure.

 my $rv = Net::SSLeay::sk_X509_push($sk_x509, $x509);
 # $sk_x509 - value corresponding to openssl's STACK_OF(X509) structure
 # $x509 - value corresponding to openssl's X509 structure
 #
 # returns: 1 if successful, 0 if unsuccessful

=back

=head3 Low level API: X509_REQ_* related functions

=over

=item * X509_REQ_new

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Creates a new X509_REQ structure.

 my $rv = Net::SSLeay::X509_REQ_new();
 #
 # returns: value corresponding to openssl's X509_REQ structure (0 on failure)

=item * X509_REQ_free

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Free an allocated X509_REQ structure.

 Net::SSLeay::X509_REQ_free($x);
 # $x - value corresponding to openssl's X509_REQ structure
 #
 # returns: no return value

=item * X509_REQ_add1_attr_by_NID

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Adds an attribute whose name is defined by a NID $nid. The field value to be added is in $bytes.

 my $rv = Net::SSLeay::X509_REQ_add1_attr_by_NID($req, $nid, $type, $bytes);
 # $req - value corresponding to openssl's X509_REQ structure
 # $nid - (integer) NID value
 # $type - (integer) type of data in $bytes (see below)
 # $bytes - data to be set
 #
 # returns: 1 on success, 0 on failure

 # values for $type - use constants:
 &Net::SSLeay::MBSTRING_UTF8     - $bytes contains utf8 encoded data
 &Net::SSLeay::MBSTRING_ASC      - $bytes contains ASCII data

=item * X509_REQ_digest

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Computes digest/fingerprint of X509_REQ $data using $type hash function.

 my $digest_value = Net::SSLeay::X509_REQ_digest($data, $type);
 # $data - value corresponding to openssl's X509_REQ structure
 # $type - value corresponding to openssl's EVP_MD structure - e.g. got via EVP_get_digestbyname()
 #
 # returns: hash value (binary)

 #to get printable (hex) value of digest use:
 print unpack('H*', $digest_value);

=item * X509_REQ_get_attr_by_NID

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Retrieve the next index matching $nid after $lastpos ($lastpos should initially be set to -1).

 my $rv = Net::SSLeay::X509_REQ_get_attr_by_NID($req, $nid, $lastpos=-1);
 # $req - value corresponding to openssl's X509_REQ structure
 # $nid - (integer) NID value
 # $lastpos - [optional] (integer) index where to start search (default -1)
 #
 # returns: index (-1 if there are no more entries)

Note: use L</P_X509_REQ_get_attr> to get the actual attribute value - e.g.

 my $index = Net::SSLeay::X509_REQ_get_attr_by_NID($req, $nid);
 my @attr_values = Net::SSLeay::P_X509_REQ_get_attr($req, $index);

=item * X509_REQ_get_attr_by_OBJ

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Retrieve the next index matching $obj after $lastpos ($lastpos should initially be set to -1).

 my $rv = Net::SSLeay::X509_REQ_get_attr_by_OBJ($req, $obj, $lastpos=-1);
 # $req - value corresponding to openssl's X509_REQ structure
 # $obj - value corresponding to openssl's ASN1_OBJECT structure
 # $lastpos - [optional] (integer) index where to start search (default -1)
 #
 # returns: index (-1 if there are no more entries)

Note: use L</P_X509_REQ_get_attr> to get the actual attribute value - e.g.

 my $index = Net::SSLeay::X509_REQ_get_attr_by_NID($req, $nid);
 my @attr_values = Net::SSLeay::P_X509_REQ_get_attr($req, $index);

=item * X509_REQ_get_attr_count

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns the total number of attributes in $req.

 my $rv = Net::SSLeay::X509_REQ_get_attr_count($req);
 # $req - value corresponding to openssl's X509_REQ structure
 #
 # returns: (integer) items count

=item * X509_REQ_get_pubkey

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns public key corresponding to given X509_REQ object $x.

 my $rv = Net::SSLeay::X509_REQ_get_pubkey($x);
 # $x - value corresponding to openssl's X509_REQ structure
 #
 # returns: value corresponding to openssl's EVP_PKEY structure (0 on failure)

=item * X509_REQ_get_subject_name

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns X509_NAME object corresponding to subject name of given X509_REQ object $x.

 my $rv = Net::SSLeay::X509_REQ_get_subject_name($x);
 # $x - value corresponding to openssl's X509_REQ structure
 #
 # returns: value corresponding to openssl's X509_NAME structure (0 on failure)

=item * X509_REQ_get_version

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns 'version' value for given X509_REQ object $x.

 my $rv = Net::SSLeay::X509_REQ_get_version($x);
 # $x - value corresponding to openssl's X509_REQ structure
 #
 # returns: (integer) version e.g. 0 = "version 1"

=item * X509_REQ_set_pubkey

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Sets public key of given X509_REQ object $x to $pkey.

 my $rv = Net::SSLeay::X509_REQ_set_pubkey($x, $pkey);
 # $x - value corresponding to openssl's X509_REQ structure
 # $pkey - value corresponding to openssl's EVP_PKEY structure
 #
 # returns: 1 on success, 0 on failure

=item * X509_REQ_set_subject_name

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Sets subject name of given X509_REQ object $x to X509_NAME object $name.

 my $rv = Net::SSLeay::X509_REQ_set_subject_name($x, $name);
 # $x - value corresponding to openssl's X509_REQ structure
 # $name - value corresponding to openssl's X509_NAME structure
 #
 # returns: 1 on success, 0 on failure

=item * X509_REQ_set_version

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Sets 'version' of given X509_REQ object $x to $version.

 my $rv = Net::SSLeay::X509_REQ_set_version($x, $version);
 # $x - value corresponding to openssl's X509_REQ structure
 # $version - (integer) e.g. 0 = "version 1"
 #
 # returns: 1 on success, 0 on failure

=item * X509_REQ_sign

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Sign X509_REQ object $x with private key $pk (using digest algorithm $md).

 my $rv = Net::SSLeay::X509_REQ_sign($x, $pk, $md);
 # $x - value corresponding to openssl's X509_REQ structure
 # $pk - value corresponding to openssl's EVP_PKEY structure (requestor's private key)
 # $md - value corresponding to openssl's EVP_MD structure
 #
 # returns: 1 on success, 0 on failure

=item * X509_REQ_verify

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Verifies X509_REQ object $x using public key $r (pubkey of requesting party).

 my $rv = Net::SSLeay::X509_REQ_verify($x, $r);
 # $x - value corresponding to openssl's X509_REQ structure
 # $r - value corresponding to openssl's EVP_PKEY structure
 #
 # returns: 0 - verify failure, 1 - verify OK, <0 - error

=item * P_X509_REQ_add_extensions

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Adds one or more X509 extensions to X509_REQ object $x.

 my $rv = Net::SSLeay::P_X509_REQ_add_extensions($x, $nid, $value);
 # $x - value corresponding to openssl's X509_REQ structure
 # $nid - NID identifying extension to be set
 # $value - extension value
 #
 # returns: 1 on success, 0 on failure

You can set more extensions at once:

 my $rv = Net::SSLeay::P_X509_REQ_add_extensions($x509_req,
            &Net::SSLeay::NID_key_usage => 'digitalSignature,keyEncipherment',
            &Net::SSLeay::NID_basic_constraints => 'CA:FALSE',
            &Net::SSLeay::NID_ext_key_usage => 'serverAuth,clientAuth',
            &Net::SSLeay::NID_netscape_cert_type => 'server',
            &Net::SSLeay::NID_subject_alt_name => 'DNS:s1.com,DNS:s2.com',
            &Net::SSLeay::NID_crl_distribution_points => 'URI:http://pki.com/crl1,URI:http://pki.com/crl2',
          );

=item * P_X509_REQ_get_attr

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before; requires at least openssl-0.9.7

Returns attribute value for X509_REQ's attribute at index $n.

 Net::SSLeay::P_X509_REQ_get_attr($req, $n);
 # $req - value corresponding to openssl's X509_REQ structure
 # $n - (integer) attribute index
 #
 # returns: value corresponding to openssl's ASN1_STRING structure

=back

=head3 Low level API: X509_CRL_* related functions

=over

=item * X509_CRL_new

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Creates a new X509_CRL structure.

 my $rv = Net::SSLeay::X509_CRL_new();
 #
 # returns: value corresponding to openssl's X509_CRL structure (0 on failure)

=item * X509_CRL_free

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Free an allocated X509_CRL structure.

 Net::SSLeay::X509_CRL_free($x);
 # $x - value corresponding to openssl's X509_CRL structure
 #
 # returns: no return value

=item * X509_CRL_digest

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Computes digest/fingerprint of X509_CRL $data using $type hash function.

 my $digest_value = Net::SSLeay::X509_CRL_digest($data, $type);
 # $data - value corresponding to openssl's X509_CRL structure
 # $type - value corresponding to openssl's EVP_MD structure - e.g. got via EVP_get_digestbyname()
 #
 # returns: hash value (binary)

Example:

 my $x509_crl
 my $md = Net::SSLeay::EVP_get_digestbyname("sha1");
 my $digest_value = Net::SSLeay::X509_CRL_digest($x509_crl, $md);
 #to get printable (hex) value of digest use:
 print "digest=", unpack('H*', $digest_value), "\n";

=item * X509_CRL_get_ext

B<COMPATIBILITY:> not available in Net-SSLeay-1.54 and before

Returns X509_EXTENSION from $x509 based on given position/index.

 my $rv = Net::SSLeay::X509_CRL_get_ext($x509, $index);
 # $x509 - value corresponding to openssl's X509_CRL structure
 # $index - (integer) position/index of extension within $x509
 #
 # returns: value corresponding to openssl's X509_EXTENSION structure (0 on failure)

=item * X509_CRL_get_ext_by_NID

B<COMPATIBILITY:> not available in Net-SSLeay-1.54 and before

Returns X509_EXTENSION from $x509 based on given NID.

 my $rv = Net::SSLeay::X509_CRL_get_ext_by_NID($x509, $nid, $loc);
 # $x509 - value corresponding to openssl's X509_CRL structure
 # $nid - (integer) NID value
 # $loc - (integer) position to start lookup at
 #
 # returns: position/index of extension, negative value on error
 #          call Net::SSLeay::X509_CRL_get_ext($x509, $rv) to get the actual extension

=item * X509_CRL_get_ext_count

B<COMPATIBILITY:> not available in Net-SSLeay-1.54 and before

Returns the total number of extensions in X509_CRL object $x.

 my $rv = Net::SSLeay::X509_CRL_get_ext_count($x);
 # $x - value corresponding to openssl's X509_CRL structure
 #
 # returns: count of extensions

=item * X509_CRL_get_issuer

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns X509_NAME object corresponding to the issuer of X509_CRL $x.

 my $rv = Net::SSLeay::X509_CRL_get_issuer($x);
 # $x - value corresponding to openssl's X509_CRL structure
 #
 # returns: value corresponding to openssl's X509_NAME structure (0 on failure)

See other C<X509_NAME_*> functions to get more info from X509_NAME structure.

=item * X509_CRL_get_lastUpdate

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns 'lastUpdate' date-time value of X509_CRL object $x.

 my $rv = Net::SSLeay::X509_CRL_get_lastUpdate($x);
 # $x - value corresponding to openssl's X509_CRL structure
 #
 # returns: value corresponding to openssl's ASN1_TIME structure (0 on failure)

=item * X509_CRL_get_nextUpdate

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns 'nextUpdate' date-time value of X509_CRL object $x.

 my $rv = Net::SSLeay::X509_CRL_get_nextUpdate($x);
 # $x - value corresponding to openssl's X509_CRL structure
 #
 # returns: value corresponding to openssl's ASN1_TIME structure (0 on failure)

=item * X509_CRL_get_version

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns 'version' value of given X509_CRL structure $x.

 my $rv = Net::SSLeay::X509_CRL_get_version($x);
 # $x - value corresponding to openssl's X509_CRL structure
 #
 # returns: (integer) version

=item * X509_CRL_set_issuer_name

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before; requires at least openssl-0.9.7

Sets the issuer of X509_CRL object $x to X509_NAME object $name.

 my $rv = Net::SSLeay::X509_CRL_set_issuer_name($x, $name);
 # $x - value corresponding to openssl's X509_CRL structure
 # $name - value corresponding to openssl's X509_NAME structure
 #
 # returns: 1 on success, 0 on failure

=item * X509_CRL_set_lastUpdate

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before; requires at least openssl-0.9.7

Sets 'lastUpdate' value of X509_CRL object $x to $tm.

 my $rv = Net::SSLeay::X509_CRL_set_lastUpdate($x, $tm);
 # $x - value corresponding to openssl's X509_CRL structure
 # $tm - value corresponding to openssl's ASN1_TIME structure
 #
 # returns: 1 on success, 0 on failure

=item * X509_CRL_set_nextUpdate

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before; requires at least openssl-0.9.7

Sets 'nextUpdate' value of X509_CRL object $x to $tm.

 my $rv = Net::SSLeay::X509_CRL_set_nextUpdate($x, $tm);
 # $x - value corresponding to openssl's X509_CRL structure
 # $tm - value corresponding to openssl's ASN1_TIME structure
 #
 # returns: 1 on success, 0 on failure

=item * X509_CRL_set_version

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before; requires at least openssl-0.9.7

Sets 'version' value of given X509_CRL structure $x to $version.

 my $rv = Net::SSLeay::X509_CRL_set_version($x, $version);
 # $x - value corresponding to openssl's X509_CRL structure
 # $version - (integer) version number (1 = version 2 CRL)
 #
 # returns: 1 on success, 0 on failure

Note that if you want to use any X509_CRL extension you need to set "version 2 CRL" - C<Net::SSLeay::X509_CRL_set_version($x, 1)>.

=item * X509_CRL_sign

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Sign X509_CRL object $x with private key $pkey (using digest algorithm $md).

 my $rv = Net::SSLeay::X509_CRL_sign($x, $pkey, $md);
 # $x - value corresponding to openssl's X509_CRL structure
 # $pkey - value corresponding to openssl's EVP_PKEY structure
 # $md - value corresponding to openssl's EVP_MD structure
 #
 # returns: 1 on success, 0 on failure

=item * X509_CRL_sort

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before; requires at least openssl-0.9.7

Sorts the data of X509_CRL object so it will be written in serial number order.

 my $rv = Net::SSLeay::X509_CRL_sort($x);
 # $x - value corresponding to openssl's X509_CRL structure
 #
 # returns: 1 on success, 0 on failure

=item * X509_CRL_verify

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Verifies X509_CRL object $a using public key $r (pubkey of issuing CA).

 my $rv = Net::SSLeay::X509_CRL_verify($a, $r);
 # $a - value corresponding to openssl's X509_CRL structure
 # $r - value corresponding to openssl's EVP_PKEY structure
 #
 # returns: 0 - verify failure, 1 - verify OK, <0 - error

=item * P_X509_CRL_add_revoked_serial_hex

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before; requires at least openssl-0.9.7

Adds given serial number $serial_hex to X509_CRL object $crl.

 Net::SSLeay::P_X509_CRL_add_revoked_serial_hex($crl, $serial_hex, $rev_time, $reason_code, $comp_time);
 # $crl - value corresponding to openssl's X509_CRL structure
 # $serial_hex - string (hexadecimal) representation of serial number
 # $rev_time - (revocation time) value corresponding to openssl's ASN1_TIME structure
 # $reason_code - [optional] (integer) reason code (see below) - default 0
 # $comp_time - [optional] (compromise time) value corresponding to openssl's ASN1_TIME structure
 #
 # returns: no return value

 reason codes:
 0 - unspecified
 1 - keyCompromise
 2 - CACompromise
 3 - affiliationChanged
 4 - superseded
 5 - cessationOfOperation
 6 - certificateHold
 7 - removeFromCRL

=item * P_X509_CRL_get_serial

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before; requires at least openssl-0.9.7

Returns serial number of X509_CRL object.

 my $rv = Net::SSLeay::P_X509_CRL_get_serial($crl);
 # $crl - value corresponding to openssl's X509_CRL structure
 #
 # returns: value corresponding to openssl's ASN1_INTEGER structure (0 on failure)

=item * P_X509_CRL_set_serial

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before; requires at least openssl-0.9.7

Sets serial number of X509_CRL object to $crl_number.

 my $rv = Net::SSLeay::P_X509_CRL_set_serial($crl, $crl_number);
 # $crl - value corresponding to openssl's X509_CRL structure
 # $crl_number - value corresponding to openssl's ASN1_INTEGER structure
 #
 # returns: 1 on success, 0 on failure

=back

=head3 Low level API: X509_EXTENSION_* related functions

=over

=item * X509_EXTENSION_get_critical

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns 'critical' flag of given X509_EXTENSION object $ex.

 my $rv = Net::SSLeay::X509_EXTENSION_get_critical($ex);
 # $ex - value corresponding to openssl's X509_EXTENSION structure
 #
 # returns: (integer) 1 - critical, 0 - noncritical

=item * X509_EXTENSION_get_data

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns value (raw data) of X509_EXTENSION object $ne.

 my $rv = Net::SSLeay::X509_EXTENSION_get_data($ne);
 # $ne - value corresponding to openssl's X509_EXTENSION structure
 #
 # returns: value corresponding to openssl's ASN1_OCTET_STRING structure (0 on failure)

Note: you can use L</P_ASN1_STRING_get> to convert ASN1_OCTET_STRING into perl scalar variable.

=item * X509_EXTENSION_get_object

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns OID (ASN1_OBJECT) of X509_EXTENSION object $ne.

 my $rv = Net::SSLeay::X509_EXTENSION_get_object($ex);
 # $ex - value corresponding to openssl's X509_EXTENSION structure
 #
 # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

=item * X509V3_EXT_print

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns string representation of given X509_EXTENSION object $ext.

 Net::SSLeay::X509V3_EXT_print($ext, $flags, $utf8_decode);
 # $ext - value corresponding to openssl's X509_EXTENSION structure
 # $flags - [optional] (integer) Currently the flag argument is unused and should be set to 0
 # $utf8_decode - [optional] 0 or 1 whether the returned value should be utf8 decoded (default=0)
 #
 # returns: no return value

=item * X509V3_EXT_d2i

Parses an extension and returns its internal structure.

 my $rv = Net::SSLeay::X509V3_EXT_d2i($ext);
 # $ext - value corresponding to openssl's X509_EXTENSION structure
 #
 # returns: pointer ???

=back

=head3 Low level API: X509_NAME_* related functions

=over

=item * X509_NAME_ENTRY_get_data

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Retrieves the field value of $ne in and ASN1_STRING structure.

 my $rv = Net::SSLeay::X509_NAME_ENTRY_get_data($ne);
 # $ne - value corresponding to openssl's X509_NAME_ENTRY structure
 #
 # returns: value corresponding to openssl's ASN1_STRING structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_NAME_ENTRY_get_object.html|http://www.openssl.org/docs/crypto/X509_NAME_ENTRY_get_object.html>

=item * X509_NAME_ENTRY_get_object

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Retrieves the field name of $ne in and ASN1_OBJECT structure.

 my $rv = Net::SSLeay::X509_NAME_ENTRY_get_object($ne);
 # $ne - value corresponding to openssl's X509_NAME_ENTRY structure
 #
 # returns: value corresponding to openssl's ASN1_OBJECT structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_NAME_ENTRY_get_object.html|http://www.openssl.org/docs/crypto/X509_NAME_ENTRY_get_object.html>

=item * X509_NAME_new

B<COMPATIBILITY:> not available in Net-SSLeay-1.55 and before; requires at least openssl-0.9.5

Creates a new X509_NAME structure.
Adds a field whose name is defined by a string $field. The field value to be added is in $bytes.

 my $rv = Net::SSLeay::X509_NAME_new();
 #
 # returns: value corresponding to openssl's X509_NAME structure (0 on failure)

=item * X509_NAME_hash

B<COMPATIBILITY:> not available in Net-SSLeay-1.55 and before; requires at least openssl-0.9.5

Sort of a checksum of issuer name $name.
The result is not a full hash (e.g. sha-1), it is kind-of-a-hash truncated to the size of 'unsigned long' (32 bits).
The resulting value might differ across different openssl versions for the same X509 certificate.

 my $rv = Net::SSLeay::X509_NAME_hash($name);
 # $name - value corresponding to openssl's X509_NAME structure
 #
 # returns: number representing checksum

=item * X509_NAME_add_entry_by_txt

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before; requires at least openssl-0.9.5

Adds a field whose name is defined by a string $field. The field value to be added is in $bytes.

 my $rv = Net::SSLeay::X509_NAME_add_entry_by_txt($name, $field, $type, $bytes, $len, $loc, $set);
 # $name - value corresponding to openssl's X509_NAME structure
 # $field - (string) field definition (name) - e.g. "organizationName"
 # $type - (integer) type of data in $bytes (see below)
 # $bytes - data to be set
 # $loc - [optional] (integer) index where the new entry is inserted: if it is -1 (default) it is appended
 # $set - [optional] (integer) determines how the new type is added. If it is 0 (default) a new RDN is created
 #
 # returns: 1 on success, 0 on failure

 # values for $type - use constants:
 &Net::SSLeay::MBSTRING_UTF8     - $bytes contains utf8 encoded data
 &Net::SSLeay::MBSTRING_ASC      - $bytes contains ASCII data

Unicode note: when passing non-ascii (unicode) string in $bytes do not forget to set C<$flags = &Net::SSLeay::MBSTRING_UTF8> and encode the perl $string via C<$bytes = encode('utf-8', $string)>.

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_NAME_add_entry_by_txt.html|http://www.openssl.org/docs/crypto/X509_NAME_add_entry_by_txt.html>

=item * X509_NAME_add_entry_by_NID

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before; requires at least openssl-0.9.5

Adds a field whose name is defined by a NID $nid. The field value to be added is in $bytes.

 my $rv = Net::SSLeay::X509_NAME_add_entry_by_NID($name, $nid, $type, $bytes, $len, $loc, $set);
 # $name - value corresponding to openssl's X509_NAME structure
 # $nid - (integer) field definition - NID value
 # $type - (integer) type of data in $bytes (see below)
 # $bytes - data to be set
 # $loc - [optional] (integer) index where the new entry is inserted: if it is -1 (default) it is appended
 # $set - [optional] (integer) determines how the new type is added. If it is 0 (default) a new RDN is created
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_NAME_add_entry_by_txt.html|http://www.openssl.org/docs/crypto/X509_NAME_add_entry_by_txt.html>

=item * X509_NAME_add_entry_by_OBJ

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before; requires at least openssl-0.9.5

Adds a field whose name is defined by a object (OID) $obj . The field value to be added is in $bytes.

 my $rv = Net::SSLeay::X509_NAME_add_entry_by_OBJ($name, $obj, $type, $bytes, $len, $loc, $set);
 # $name - value corresponding to openssl's X509_NAME structure
 # $obj - field definition - value corresponding to openssl's ASN1_OBJECT structure
 # $type - (integer) type of data in $bytes (see below)
 # $bytes - data to be set
 # $loc - [optional] (integer) index where the new entry is inserted: if it is -1 (default) it is appended
 # $set - [optional] (integer) determines how the new type is added. If it is 0 (default) a new RDN is created
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_NAME_add_entry_by_txt.html|http://www.openssl.org/docs/crypto/X509_NAME_add_entry_by_txt.html>

=item * X509_NAME_cmp

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Compares two X509_NAME obejcts.

 my $rv = Net::SSLeay::X509_NAME_cmp($a, $b);
 # $a - value corresponding to openssl's X509_NAME structure
 # $b - value corresponding to openssl's X509_NAME structure
 #
 # returns: 0 if $a matches $b; non zero otherwise

=item * X509_NAME_digest

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Computes digest/fingerprint of X509_NAME $data using $type hash function.

 my $digest_value = Net::SSLeay::X509_NAME_digest($data, $type);
 # $data - value corresponding to openssl's X509_NAME structure
 # $type - value corresponding to openssl's EVP_MD structure - e.g. got via EVP_get_digestbyname()
 #
 # returns: hash value (binary)

 #to get printable (hex) value of digest use:
 print unpack('H*', $digest_value);

=item * X509_NAME_entry_count

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns the total number of entries in $name.

 my $rv = Net::SSLeay::X509_NAME_entry_count($name);
 # $name - value corresponding to openssl's X509_NAME structure
 #
 # returns: (integer) entries count

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_NAME_get_index_by_NID.html|http://www.openssl.org/docs/crypto/X509_NAME_get_index_by_NID.html>

=item * X509_NAME_get_entry

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Retrieves the X509_NAME_ENTRY from $name corresponding to index $loc. Acceptable values for $loc run
from 0 to C<Net::SSLeay::X509_NAME_entry_count($name)- 1>. The value returned is an internal pointer which must not be freed.

 my $rv = Net::SSLeay::X509_NAME_get_entry($name, $loc);
 # $name - value corresponding to openssl's X509_NAME structure
 # $loc - (integer) index of wanted entry
 #
 # returns: value corresponding to openssl's X509_NAME_ENTRY structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_NAME_get_index_by_NID.html|http://www.openssl.org/docs/crypto/X509_NAME_get_index_by_NID.html>

=item * X509_NAME_print_ex

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns a string with human readable version of $name.

 Net::SSLeay::X509_NAME_print_ex($name, $flags, $utf8_decode);
 # $name - value corresponding to openssl's X509_NAME structure
 # $flags - [optional] conversion flags (default XN_FLAG_RFC2253) - see below
 # $utf8_decode - [optional] 0 or 1 whether the returned value should be utf8 decoded (default=0)
 #
 # returns: string representation of $name

 #available conversion flags - use constants:
 &Net::SSLeay::XN_FLAG_COMPAT
 &Net::SSLeay::XN_FLAG_DN_REV
 &Net::SSLeay::XN_FLAG_DUMP_UNKNOWN_FIELDS
 &Net::SSLeay::XN_FLAG_FN_ALIGN
 &Net::SSLeay::XN_FLAG_FN_LN
 &Net::SSLeay::XN_FLAG_FN_MASK
 &Net::SSLeay::XN_FLAG_FN_NONE
 &Net::SSLeay::XN_FLAG_FN_OID
 &Net::SSLeay::XN_FLAG_FN_SN
 &Net::SSLeay::XN_FLAG_MULTILINE
 &Net::SSLeay::XN_FLAG_ONELINE
 &Net::SSLeay::XN_FLAG_RFC2253
 &Net::SSLeay::XN_FLAG_SEP_COMMA_PLUS
 &Net::SSLeay::XN_FLAG_SEP_CPLUS_SPC
 &Net::SSLeay::XN_FLAG_SEP_MASK
 &Net::SSLeay::XN_FLAG_SEP_MULTILINE
 &Net::SSLeay::XN_FLAG_SEP_SPLUS_SPC
 &Net::SSLeay::XN_FLAG_SPC_EQ

Most likely you will be fine with default:

 Net::SSLeay::X509_NAME_print_ex($name, &Net::SSLeay::XN_FLAG_RFC2253);

Or you might want RFC2253-like output without utf8 chars escaping:

 use Net::SSLeay qw/XN_FLAG_RFC2253 ASN1_STRFLGS_ESC_MSB/;
 my $flag_rfc22536_utf8 = (XN_FLAG_RFC2253) & (~ ASN1_STRFLGS_ESC_MSB);
 my $result = Net::SSLeay::X509_NAME_print_ex($name, $flag_rfc22536_utf8, 1);

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_NAME_print_ex.html|http://www.openssl.org/docs/crypto/X509_NAME_print_ex.html>

=item * X509_NAME_get_text_by_NID

Retrieves the text from the first entry in name which matches $nid, if no
such entry exists -1 is returned.

B<openssl note:> this is a legacy function which has various limitations which
makes it of minimal use in practice. It can only find the first matching
entry and will copy the contents of the field verbatim: this can be highly
confusing if the target is a multicharacter string type like a BMPString or a UTF8String.

 Net::SSLeay::X509_NAME_get_text_by_NID($name, $nid);
 # $name - value corresponding to openssl's X509_NAME structure
 # $nid - NID value (integer)
 #
 # returns: text value

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_NAME_get_index_by_NID.html|http://www.openssl.org/docs/crypto/X509_NAME_get_index_by_NID.html>

=item * X509_NAME_oneline

Return an ASCII version of $name.

 Net::SSLeay::X509_NAME_oneline($name);
 # $name - value corresponding to openssl's X509_NAME structure
 #
 # returns: (string) ASCII version of $name

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_NAME_print_ex.html|http://www.openssl.org/docs/crypto/X509_NAME_print_ex.html>

=item * sk_X509_NAME_free

Free an allocated STACK_OF(X509_NAME) structure.

 Net::SSLeay::sk_X509_NAME_free($sk);
 # $sk - value corresponding to openssl's STACK_OF(X509_NAME) structure
 #
 # returns: no return value

=item * sk_X509_NAME_num

Return number of items in STACK_OF(X509_NAME)

 my $rv = Net::SSLeay::sk_X509_NAME_num($sk);
 # $sk - value corresponding to openssl's STACK_OF(X509_NAME) structure
 #
 # returns: number of items

=item * sk_X509_NAME_value

Returns X509_NAME from position $index in STACK_OF(X509_NAME)

 my $rv = Net::SSLeay::sk_X509_NAME_value($sk, $i);
 # $sk - value corresponding to openssl's STACK_OF(X509_NAME) structure
 # $i - (integer) index/position
 #
 # returns: value corresponding to openssl's X509_NAME structure (0 on failure)

=item * add_file_cert_subjects_to_stack

Add a file of certs to a stack. All certs in $file that are not already in the $stackCAs will be added.

 my $rv = Net::SSLeay::add_file_cert_subjects_to_stack($stackCAs, $file);
 # $stackCAs - value corresponding to openssl's STACK_OF(X509_NAME) structure
 # $file - (string) filename
 #
 # returns: 1 on success, 0 on failure

=item * add_dir_cert_subjects_to_stack

Add a directory of certs to a stack. All certs in $dir that are not already in the $stackCAs will be added.

 my $rv = Net::SSLeay::add_dir_cert_subjects_to_stack($stackCAs, $dir);
 # $stackCAs - value corresponding to openssl's STACK_OF(X509_NAME) structure
 # $dir - (string) the directory to append from. All files in this directory will be examined as potential certs. Any that are acceptable to SSL_add_dir_cert_subjects_to_stack() that are not already in the stack will be included.
 #
 # returns: 1 on success, 0 on failure

=back

=head3 Low level API: X509_STORE_* related functions

=over

=item * X509_STORE_CTX_new

returns a newly initialised X509_STORE_CTX structure. 

=item * X509_STORE_CTX_init

X509_STORE_CTX_init() sets up an X509_STORE_CTX for a subsequent verification operation.
It must be called before each call to X509_verify_cert().

Net::SSLeay::X509_STORE_CTX_init($x509_store_ctx, $x509_store, $x509, $chain);

# $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure (required)
# $x509_store - value corresponding to openssl's X509_STORE structure (optional)
# $x509 - value corresponding to openssl's X509 structure (optional)
# $chain - value corresponding to openssl's STACK_OF(X509) structure (optional)

Check openssl doc L<https://www.openssl.org/docs/man1.0.2/crypto/X509_STORE_CTX_init.html|https://www.openssl.org/docs/man1.0.2/crypto/X509_STORE_CTX_init.html>

=item * X509_STORE_CTX_free

Frees an X509_STORE_CTX structure.

Net::SSLeay::X509_STORE_CTX_free($x509_store_ctx);

# $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure

=item * X509_verify_cert

The X509_verify_cert() function attempts to discover and validate a
certificate chain based on parameters in ctx. A complete description
of the process is contained in the verify(1) manual page.

If this function returns 0, use X509_STORE_CTX_get_error to get additional error
information.

my $rv = Net::SSLeay::X509_verify_cert($x509_store_ctx);
# $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
#
# returns: 1 if a complete chain can be built and validated, otherwise 0

Check openssl doc L<https://www.openssl.org/docs/manmaster/man3/X509_verify_cert.html|https://www.openssl.org/docs/manmaster/man3/X509_verify_cert.html>

=item * X509_STORE_CTX_get_current_cert

Returns the certificate in ctx which caused the error or 0 if no certificate is relevant.

 my $rv = Net::SSLeay::X509_STORE_CTX_get_current_cert($x509_store_ctx);
 # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
 #
 # returns: value corresponding to openssl's X509 structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_STORE_CTX_get_error.html|http://www.openssl.org/docs/crypto/X509_STORE_CTX_get_error.html>

=item * X509_STORE_CTX_get_error

Returns the error code of $ctx.

 my $rv = Net::SSLeay::X509_STORE_CTX_get_error($x509_store_ctx);
 # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
 #
 # returns: (integer) error code

For more info about erro code values check function L</get_verify_result>.

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_STORE_CTX_get_error.html|http://www.openssl.org/docs/crypto/X509_STORE_CTX_get_error.html>

=item * X509_STORE_CTX_get_error_depth

Returns the depth of the error. This is a non-negative integer representing
where in the certificate chain the error occurred. If it is zero it occurred
in the end entity certificate, one if it is the certificate which signed
the end entity certificate and so on.

 my $rv = Net::SSLeay::X509_STORE_CTX_get_error_depth($x509_store_ctx);
 # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
 #
 # returns: (integer) depth

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_STORE_CTX_get_error.html|http://www.openssl.org/docs/crypto/X509_STORE_CTX_get_error.html>

=item * X509_STORE_CTX_get_ex_data

Is used to retrieve the information for $idx from $x509_store_ctx.

 my $rv = Net::SSLeay::X509_STORE_CTX_get_ex_data($x509_store_ctx, $idx);
 # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
 # $idx - (integer) index for application specific data
 #
 # returns: pointer to ???

=item * X509_STORE_CTX_set_ex_data

Is used to store application data at arg for idx into $x509_store_ctx.

 my $rv = Net::SSLeay::X509_STORE_CTX_set_ex_data($x509_store_ctx, $idx, $data);
 # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
 # $idx - (integer) ???
 # $data - (pointer) ???
 #
 # returns: 1 on success, 0 on failure

=item * X509_STORE_CTX_set_cert

Sets the certificate to be verified in $x509_store_ctx to $x.

 Net::SSLeay::X509_STORE_CTX_set_cert($x509_store_ctx, $x);
 # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
 # $x - value corresponding to openssl's X509 structure
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_STORE_CTX_new.html|http://www.openssl.org/docs/crypto/X509_STORE_CTX_new.html>

=item * X509_STORE_new

Returns a newly initialized X509_STORE structure.

my $rv = Net::SSLeay::X509_STORE_new();
#
# returns: value corresponding to openssl's X509_STORE structure (0 on failure)

=item * X509_STORE_free

Frees an X509_STORE structure

Net::SSLeay::X509_STORE_free($x509_store);
# $x509_store - value corresponding to openssl's X509_STORE structure

=item * X509_STORE_add_lookup

Adds a lookup to an X509_STORE for a given lookup method.

my $method = &Net::SSLeay::X509_LOOKUP_hash_dir;
my $rv = Net::SSLeay::X509_STORE_add_lookup($x509_store, $method);
# $method - value corresponding to openssl's X509_LOOKUP_METHOD structure
# $x509_store - value corresponding to openssl's X509_STORE structure
#
# returns: value corresponding to openssl's X509_LOOKUP structure

Check openssl doc L<https://www.openssl.org/docs/man1.1.1/man3/X509_load_crl_file.html|https://www.openssl.org/docs/man1.1.1/man3/X509_load_crl_file.html>

=item * X509_STORE_CTX_set_error

Sets the error code of $ctx to $s. For example it might be used in a verification callback to set an error based on additional checks.

 Net::SSLeay::X509_STORE_CTX_set_error($x509_store_ctx, $s);
 # $x509_store_ctx - value corresponding to openssl's X509_STORE_CTX structure
 # $s - (integer) error id
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_STORE_CTX_get_error.html|http://www.openssl.org/docs/crypto/X509_STORE_CTX_get_error.html>

=item * X509_STORE_add_cert

Adds X509 certificate $x into the X509_STORE $store.

 my $rv = Net::SSLeay::X509_STORE_add_cert($store, $x);
 # $store - value corresponding to openssl's X509_STORE structure
 # $x - value corresponding to openssl's X509 structure
 #
 # returns: 1 on success, 0 on failure

=item * X509_STORE_add_crl

Adds X509 CRL $x into the X509_STORE $store.

 my $rv = Net::SSLeay::X509_STORE_add_crl($store, $x);
 # $store - value corresponding to openssl's X509_STORE structure
 # $x - value corresponding to openssl's X509_CRL structure
 #
 # returns: 1 on success, 0 on failure

=item * X509_STORE_set1_param

??? (more info needed)

 my $rv = Net::SSLeay::X509_STORE_set1_param($store, $pm);
 # $store - value corresponding to openssl's X509_STORE structure
 # $pm - value corresponding to openssl's X509_VERIFY_PARAM structure
 #
 # returns: 1 on success, 0 on failure

=item * X509_LOOKUP_hash_dir

Returns an X509_LOOKUP structure that instructs an X509_STORE to
load files from a directory containing certificates with filenames
in the format I<hash.N> or crls with filenames in the format I<hash.>B<r>I<N>

my $rv = Net::SSLeay::X509_LOOKUP_hash_dir();
#
# returns: value corresponding to openssl's X509_LOOKUP_METHOD structure, with the hashed directory method

Check openssl doc L<https://www.openssl.org/docs/man1.1.1/man3/X509_load_crl_file.html|https://www.openssl.org/docs/man1.1.1/man3/X509_load_crl_file.html>

=item * X509_LOOKUP_add_dir

Add a directory to an X509_LOOKUP structure, usually obtained from
X509_STORE_add_lookup.

my $method = &Net::SSLeay::X509_LOOKUP_hash_dir;
my $lookup = Net::SSLeay::X509_STORE_add_lookup($x509_store, $method);
my $type = &Net::SSLeay::X509_FILETYPE_PEM;
Net::SSLeay::X509_LOOKUP_add_dir($lookup, $dir, $type);
# $lookup - value corresponding to openssl's X509_LOOKUP structure
# $dir - string path to a directory
s# $type - constant corresponding to the type of file in the directory - can be X509_FILETYPE_PEM, X509_FILETYPE_DEFAULT, or X509_FILETYPE_ASN1

=item * X509_STORE_set_flags

 Net::SSLeay::X509_STORE_set_flags($ctx, $flags);
 # $ctx - value corresponding to openssl's X509_STORE structure
 # $flags - (unsigned long) flags to be set (bitmask)
 #
 # returns: no return value

 #to create $flags value use corresponding constants like
 $flags = Net::SSLeay::X509_V_FLAG_CRL_CHECK();

For more details about $flags bitmask see L</X509_VERIFY_PARAM_set_flags>.

=item * X509_STORE_set_purpose

 Net::SSLeay::X509_STORE_set_purpose($ctx, $purpose);
 # $ctx - value corresponding to openssl's X509_STORE structure
 # $purpose - (integer) purpose identifier
 #
 # returns: no return value

For more details about $purpose identifier check L</CTX_set_purpose>.

=item * X509_STORE_set_trust

 Net::SSLeay::X509_STORE_set_trust($ctx, $trust);
 # $ctx - value corresponding to openssl's X509_STORE structure
 # $trust - (integer) trust identifier
 #
 # returns: no return value

For more details about $trust identifier check L</CTX_set_trust>.

=back

=head3 Low Level API: X509_INFO related functions

=over

=item * sk_X509_INFO_num

Returns the number of values in a STACK_OF(X509_INFO) structure.

 my $rv = Net::SSLeay::sk_X509_INFO_num($sk_x509_info);
 # $sk_x509_info - value corresponding to openssl's STACK_OF(X509_INFO) structure
 #
 # returns: number of values in $sk_X509_info

=item * sk_X509_INFO_value

Returns the value of a STACK_OF(X509_INFO) structure at a given index.

 my $rv = Net::SSLeay::sk_X509_INFO_value($sk_x509_info, $index);
 # $sk_x509_info - value corresponding to openssl's STACK_OF(X509_INFO) structure
 # $index - index into the stack
 #
 # returns: value corresponding to openssl's X509_INFO structure at the given index

=item * P_X509_INFO_get_x509

Returns the X509 structure stored in an X509_INFO structure.

 my $rv = Net::SSLeay::P_X509_INFO_get_x509($x509_info);
 # $x509_info - value corresponding to openssl's X509_INFO structure
 #
 # returns: value corresponding to openssl's X509 structure

=back

=head3 Low level API: X509_VERIFY_PARAM_* related functions

=over

=item * X509_VERIFY_PARAM_add0_policy

Enables policy checking (it is disabled by default) and adds $policy to the acceptable policy set.

 my $rv = Net::SSLeay::X509_VERIFY_PARAM_add0_policy($param, $policy);
 # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
 # $policy - value corresponding to openssl's ASN1_OBJECT structure
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html|http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

=item * X509_VERIFY_PARAM_add0_table

??? (more info needed)

 my $rv = Net::SSLeay::X509_VERIFY_PARAM_add0_table($param);
 # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
 #
 # returns: 1 on success, 0 on failure

=item * X509_VERIFY_PARAM_add1_host

B<COMPATIBILITY:> not available in Net-SSLeay-1.82 and before; requires at least OpenSSL 1.0.2

Adds an additional reference identifier that can match the peer's certificate.

 my $rv = Net::SSLeay::X509_VERIFY_PARAM_add1_host($param, $name);
 # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
 # $name - (string) name to be set
 #
 # returns: 1 on success, 0 on failure

See also OpenSSL docs, L</X509_VERIFY_PARAM_set1_host> and
L</X509_VERIFY_PARAM_set_hostflags> for more information, including
wildcard matching.

Check openssl doc L<https://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html|https://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

=item * X509_VERIFY_PARAM_clear_flags

Clears the flags $flags in param.

 my $rv = Net::SSLeay::X509_VERIFY_PARAM_clear_flags($param, $flags);
 # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
 # $flags - (unsigned long) flags to be set (bitmask)
 #
 # returns: 1 on success, 0 on failure

For more details about $flags bitmask see L</X509_VERIFY_PARAM_set_flags>.

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html|http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

=item * X509_VERIFY_PARAM_free

Frees up the X509_VERIFY_PARAM structure.

 Net::SSLeay::X509_VERIFY_PARAM_free($param);
 # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
 #
 # returns: no return value

=item * X509_VERIFY_PARAM_get0_peername

B<COMPATIBILITY:> not available in Net-SSLeay-1.82 and before; requires at least OpenSSL 1.0.2

Returns the DNS hostname or subject CommonName from the peer certificate that matched one of the reference identifiers.

 my $rv = Net::SSLeay::X509_VERIFY_PARAM_get0_peername($param);
 # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
 #
 # returns: (string) name e.g. '*.example.com' or undef

Check openssl doc L<https://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html|https://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

=item * X509_VERIFY_PARAM_get_depth

Returns the current verification depth.

 my $rv = Net::SSLeay::X509_VERIFY_PARAM_get_depth($param);
 # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
 #
 # returns: (ineger) depth

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html|http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

=item * X509_VERIFY_PARAM_get_flags

Returns the current verification flags.

 my $rv = Net::SSLeay::X509_VERIFY_PARAM_get_flags($param);
 # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
 #
 # returns: (unsigned long) flags to be set (bitmask)

For more details about returned flags bitmask see L</X509_VERIFY_PARAM_set_flags>.

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html|http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

=item * X509_VERIFY_PARAM_set_flags

 my $rv = Net::SSLeay::X509_VERIFY_PARAM_set_flags($param, $flags);
 # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
 # $flags - (unsigned long) flags to be set (bitmask)
 #
 # returns: 1 on success, 0 on failure

 #to create $flags value use corresponding constants like
 $flags = Net::SSLeay::X509_V_FLAG_CRL_CHECK();

For more details about $flags bitmask, see the OpenSSL docs below.

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html|http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

=item * X509_VERIFY_PARAM_inherit

??? (more info needed)

 my $rv = Net::SSLeay::X509_VERIFY_PARAM_inherit($to, $from);
 # $to - value corresponding to openssl's X509_VERIFY_PARAM structure
 # $from - value corresponding to openssl's X509_VERIFY_PARAM structure
 #
 # returns: 1 on success, 0 on failure

=item * X509_VERIFY_PARAM_lookup

Finds X509_VERIFY_PARAM by name.

 my $rv = Net::SSLeay::X509_VERIFY_PARAM_lookup($name);
 # $name - (string) name we want to find
 #
 # returns: value corresponding to openssl's X509_VERIFY_PARAM structure (0 on failure)

=item * X509_VERIFY_PARAM_new

Creates a new X509_VERIFY_PARAM structure.

 my $rv = Net::SSLeay::X509_VERIFY_PARAM_new();
 #
 # returns: value corresponding to openssl's X509_VERIFY_PARAM structure (0 on failure)

=item * X509_VERIFY_PARAM_set1

Sets the name of X509_VERIFY_PARAM structure $to to the same value
as the name of X509_VERIFY_PARAM structure $from.

 my $rv = Net::SSLeay::X509_VERIFY_PARAM_set1($to, $from);
 # $to - value corresponding to openssl's X509_VERIFY_PARAM structure
 # $from - value corresponding to openssl's X509_VERIFY_PARAM structure
 #
 # returns: 1 on success, 0 on failure

=item * X509_VERIFY_PARAM_set1_email

B<COMPATIBILITY:> not available in Net-SSLeay-1.82 and before; requires at least OpenSSL 1.0.2

Sets the expected RFC822 email address to email.

 my $rv = Net::SSLeay::X509_VERIFY_PARAM_set1_email($param, $email);
 # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
 # $email - (string) email to be set
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<https://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html|https://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

=item * X509_VERIFY_PARAM_set1_host

B<COMPATIBILITY:> not available in Net-SSLeay-1.82 and before; requires at least OpenSSL 1.0.2

Sets the expected DNS hostname to name clearing any previously specified host name or names.

 my $rv = Net::SSLeay::X509_VERIFY_PARAM_set1_host($param, $name);
 # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
 # $name - (string) name to be set
 #
 # returns: 1 on success, 0 on failure

See also OpenSSL docs, L</X509_VERIFY_PARAM_add1_host> and
L</X509_VERIFY_PARAM_set_hostflags> for more information, including
wildcard matching.

Check openssl doc L<https://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html|https://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

=item * X509_VERIFY_PARAM_set1_ip

B<COMPATIBILITY:> not available in Net-SSLeay-1.82 and before; requires at least OpenSSL 1.0.2

Sets the expected IP address to ip.

 my $rv = Net::SSLeay::X509_VERIFY_PARAM_set1_ip($param, $ip);
 # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
 # $ip - (binary) 4 octet IPv4 or 16 octet IPv6 address
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<https://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html|https://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

=item * X509_VERIFY_PARAM_set1_ip_asc

B<COMPATIBILITY:> not available in Net-SSLeay-1.82 and before; requires at least OpenSSL 1.0.2

Sets the expected IP address to ipasc.

 my $rv = Net::SSLeay::X509_VERIFY_PARAM_set1_asc($param, $ipasc);
 # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
 # $ip - (string) IPv4 or IPv6 address
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<https://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html|https://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

=item * X509_VERIFY_PARAM_set1_name

Sets the name of X509_VERIFY_PARAM structure $param to $name.

 my $rv = Net::SSLeay::X509_VERIFY_PARAM_set1_name($param, $name);
 # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
 # $name - (string) name to be set
 #
 # returns: 1 on success, 0 on failure

=item * X509_VERIFY_PARAM_set1_policies

Enables policy checking (it is disabled by default) and sets the acceptable policy set to policies.
Any existing policy set is cleared. The policies parameter can be 0 to clear an existing policy set.

 my $rv = Net::SSLeay::X509_VERIFY_PARAM_set1_policies($param, $policies);
 # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
 # $policies - value corresponding to openssl's STACK_OF(ASN1_OBJECT) structure
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html|http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

=item * X509_VERIFY_PARAM_set_depth

Sets the maximum verification depth to depth. That is the maximum number of untrusted CA certificates that can appear in a chain.

 Net::SSLeay::X509_VERIFY_PARAM_set_depth($param, $depth);
 # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
 # $depth - (integer) depth to be set
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html|http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

=item * X509_VERIFY_PARAM_set_hostflags

 Net::SSLeay::X509_VERIFY_PARAM_set_hostflags($param, $flags);
 # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
 # $flags - (unsigned int) flags to be set (bitmask)
 #
 # returns: no return value

See also OpenSSL docs,  L</X509_VERIFY_PARAM_add1_host> and L</X509_VERIFY_PARAM_set1_host> for more information.
The flags for controlling wildcard checks and other features are defined in OpenSSL docs.

Check openssl doc L<https://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html|https://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

=item * X509_VERIFY_PARAM_set_purpose

Sets the verification purpose in $param to $purpose. This determines the acceptable purpose
of the certificate chain, for example SSL client or SSL server.

 my $rv = Net::SSLeay::X509_VERIFY_PARAM_set_purpose($param, $purpose);
 # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
 # $purpose - (integer) purpose identifier
 #
 # returns: 1 on success, 0 on failure

For more details about $purpose identifier check L</CTX_set_purpose>.

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html|http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

=item * X509_VERIFY_PARAM_set_time

Sets the verification time in $param to $t. Normally the current time is used.

 Net::SSLeay::X509_VERIFY_PARAM_set_time($param, $t);
 # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
 # $t - (time_t) time in seconds since 1.1.1970
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html|http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

=item * X509_VERIFY_PARAM_set_trust

Sets the trust setting in $param to $trust.

 my $rv = Net::SSLeay::X509_VERIFY_PARAM_set_trust($param, $trust);
 # $param - value corresponding to openssl's X509_VERIFY_PARAM structure
 # $trust - (integer) trust identifier
 #
 # returns: 1 on success, 0 on failure

For more details about $trust identifier check L</CTX_set_trust>.

Check openssl doc L<http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html|http://www.openssl.org/docs/crypto/X509_VERIFY_PARAM_set_flags.html>

=item * X509_VERIFY_PARAM_table_cleanup

??? (more info needed)

 Net::SSLeay::X509_VERIFY_PARAM_table_cleanup();
 #
 # returns: no return value

=back

=head3 Low level API: Cipher (EVP_CIPHER_*) related functions

=over

=item * EVP_get_cipherbyname

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before

Returns an EVP_CIPHER structure when passed a cipher name.

 my $rv = Net::SSLeay::EVP_get_cipherbyname($name);
 # $name - (string) cipher name e.g. 'aes-128-cbc', 'camellia-256-ecb', 'des-ede', ...
 #
 # returns: value corresponding to openssl's EVP_CIPHER structure

Check openssl doc L<http://www.openssl.org/docs/crypto/EVP_EncryptInit.html|http://www.openssl.org/docs/crypto/EVP_EncryptInit.html>

=back

=head3 Low level API: Digest (EVP_MD_*) related functions

=over

=item * OpenSSL_add_all_digests

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before

 Net::SSLeay::OpenSSL_add_all_digests();
 # no args, no return value

http://www.openssl.org/docs/crypto/OpenSSL_add_all_algorithms.html

=item * P_EVP_MD_list_all

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before; requires at least openssl-1.0.0

B<NOTE:> Does not exactly correspond to any low level API function

 my $rv = Net::SSLeay::P_EVP_MD_list_all();
 #
 # returns: arrayref - list of available digest names

The returned digest names correspond to values expected by L</EVP_get_digestbyname>.

Note that some of the digests are available by default and some only after calling L</OpenSSL_add_all_digests>.

=item * EVP_get_digestbyname

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before

 my $rv = Net::SSLeay::EVP_get_digestbyname($name);
 # $name - string with digest name
 #
 # returns: value corresponding to openssl's EVP_MD structure

The $name param can be:

 md2
 md4
 md5
 mdc2
 ripemd160
 sha
 sha1
 sha224
 sha256
 sha512
 whirlpool

Or better check the supported digests by calling L</P_EVP_MD_list_all>.

=item * EVP_MD_type

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before

 my $rv = Net::SSLeay::EVP_MD_type($md);
 # $md - value corresponding to openssl's EVP_MD structure
 #
 # returns: the NID (integer) of the OBJECT IDENTIFIER representing the given message digest

=item * EVP_MD_size

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before

 my $rv = Net::SSLeay::EVP_MD_size($md);
 # $md - value corresponding to openssl's EVP_MD structure
 #
 # returns: the size of the message digest in bytes (e.g. 20 for SHA1)

=item * EVP_MD_CTX_md

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before; requires at least openssl-0.9.7

 Net::SSLeay::EVP_MD_CTX_md($ctx);
 # $ctx - value corresponding to openssl's EVP_MD_CTX structure
 #
 # returns: value corresponding to openssl's EVP_MD structure

=item * EVP_MD_CTX_create

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before; requires at least openssl-0.9.7

Allocates, initializes and returns a digest context.

 my $rv = Net::SSLeay::EVP_MD_CTX_create();
 #
 # returns: value corresponding to openssl's EVP_MD_CTX structure

The complete idea behind EVP_MD_CTX looks like this example:

  Net::SSLeay::OpenSSL_add_all_digests();

  my $md = Net::SSLeay::EVP_get_digestbyname("sha1");
  my $ctx = Net::SSLeay::EVP_MD_CTX_create();
  Net::SSLeay::EVP_DigestInit($ctx, $md);

  while(my $chunk = get_piece_of_data()) {
    Net::SSLeay::EVP_DigestUpdate($ctx,$chunk);
  }

  my $result = Net::SSLeay::EVP_DigestFinal($ctx);
  Net::SSLeay::EVP_MD_CTX_destroy($ctx);

  print "digest=", unpack('H*', $result), "\n"; #print hex value

=item * EVP_DigestInit_ex

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before; requires at least openssl-0.9.7

Sets up digest context $ctx to use a digest $type from ENGINE $impl, $ctx must be
initialized before calling this function, type will typically be supplied by a function
such as L</EVP_get_digestbyname>. If $impl is 0 then the default implementation of digest $type is used.

 my $rv = Net::SSLeay::EVP_DigestInit_ex($ctx, $type, $impl);
 # $ctx  - value corresponding to openssl's EVP_MD_CTX structure
 # $type - value corresponding to openssl's EVP_MD structure
 # $impl - value corresponding to openssl's ENGINE structure
 #
 # returns: 1 for success and 0 for failure

=item * EVP_DigestInit

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before; requires at least openssl-0.9.7

Behaves in the same way as L</EVP_DigestInit_ex> except the passed context $ctx does not have
to be initialized, and it always uses the default digest implementation.

 my $rv = Net::SSLeay::EVP_DigestInit($ctx, $type);
 # $ctx - value corresponding to openssl's EVP_MD_CTX structure
 # $type - value corresponding to openssl's EVP_MD structure
 #
 # returns: 1 for success and 0 for failure

=item * EVP_MD_CTX_destroy

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before; requires at least openssl-0.9.7

Cleans up digest context $ctx and frees up the space allocated to it, it should be
called only on a context created using L</EVP_MD_CTX_create>.

 Net::SSLeay::EVP_MD_CTX_destroy($ctx);
 # $ctx - value corresponding to openssl's EVP_MD_CTX structure
 #
 # returns: no return value

=item * EVP_DigestUpdate

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before; requires at least openssl-0.9.7

 my $rv = Net::SSLeay::EVP_DigestUpdate($ctx, $data);
 # $ctx  - value corresponding to openssl's EVP_MD_CTX structure
 # $data - data to be hashed
 #
 # returns: 1 for success and 0 for failure

=item * EVP_DigestFinal_ex

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before; requires at least openssl-0.9.7

Retrieves the digest value from $ctx. After calling L</EVP_DigestFinal_ex> no
additional calls to L</EVP_DigestUpdate> can be made, but
L</EVP_DigestInit_ex> can be called to initialize a new digest operation.

 my $digest_value = Net::SSLeay::EVP_DigestFinal_ex($ctx);
 # $ctx - value corresponding to openssl's EVP_MD_CTX structure
 #
 # returns: hash value (binary)

 #to get printable (hex) value of digest use:
 print unpack('H*', $digest_value);

=item * EVP_DigestFinal

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before; requires at least openssl-0.9.7

Similar to L</EVP_DigestFinal_ex> except the digest context ctx is automatically cleaned up.

 my $rv = Net::SSLeay::EVP_DigestFinal($ctx);
 # $ctx - value corresponding to openssl's EVP_MD_CTX structure
 #
 # returns: hash value (binary)

 #to get printable (hex) value of digest use:
 print unpack('H*', $digest_value);

=item * MD2

B<COMPATIBILITY:> no supported by default in openssl-1.0.0

Computes MD2 from given $data (all data needs to be loaded into memory)

 my $digest = Net::SSLeay::MD2($data);
 print "digest(hexadecimal)=", unpack('H*', $digest);

=item * MD4

Computes MD4 from given $data (all data needs to be loaded into memory)

 my $digest = Net::SSLeay::MD4($data);
 print "digest(hexadecimal)=", unpack('H*', $digest);

=item * MD5

Computes MD5 from given $data (all data needs to be loaded into memory)

 my $digest = Net::SSLeay::MD5($data);
 print "digest(hexadecimal)=", unpack('H*', $digest);

=item * RIPEMD160

Computes RIPEMD160 from given $data (all data needs to be loaded into memory)

 my $digest = Net::SSLeay::RIPEMD160($data);
 print "digest(hexadecimal)=", unpack('H*', $digest);

=item * SHA1

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before

Computes SHA1 from given $data (all data needs to be loaded into memory)

 my $digest = Net::SSLeay::SHA1($data);
 print "digest(hexadecimal)=", unpack('H*', $digest);

=item * SHA256

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before; requires at least openssl-0.9.8

Computes SHA256 from given $data (all data needs to be loaded into memory)

 my $digest = Net::SSLeay::SHA256($data);
 print "digest(hexadecimal)=", unpack('H*', $digest);

=item * SHA512

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before; requires at least openssl-0.9.8

Computes SHA512 from given $data (all data needs to be loaded into memory)

 my $digest = Net::SSLeay::SHA512($data);
 print "digest(hexadecimal)=", unpack('H*', $digest);

=item * EVP_Digest

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before; requires at least openssl-0.9.7

Computes "any" digest from given $data (all data needs to be loaded into memory)

 my $md = Net::SSLeay::EVP_get_digestbyname("sha1"); #or any other algorithm
 my $digest = Net::SSLeay::EVP_Digest($data, $md);
 print "digest(hexadecimal)=", unpack('H*', $digest);

=item * EVP_sha1

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before

 my $md = Net::SSLeay::EVP_sha1();
 #
 # returns: value corresponding to openssl's EVP_MD structure

=item * EVP_sha256

B<COMPATIBILITY:> requires at least openssl-0.9.8

 my $md = Net::SSLeay::EVP_sha256();
 #
 # returns: value corresponding to openssl's EVP_MD structure

=item * EVP_sha512

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before; requires at least openssl-0.9.8

 my $md = Net::SSLeay::EVP_sha512();
 #
 # returns: value corresponding to openssl's EVP_MD structure

=item * EVP_add_digest

 my $rv = Net::SSLeay::EVP_add_digest($digest);
 # $digest - value corresponding to openssl's EVP_MD structure
 #
 # returns: 1 on success, 0 otherwise

=back

=head3 Low level API: CIPHER_* related functions

=over

=item * CIPHER_get_name

B<COMPATIBILITY:> not available in Net-SSLeay-1.42 and before

Returns name of the cipher used.

 my $rv = Net::SSLeay::CIPHER_description($cipher);
 # $cipher - value corresponding to openssl's SSL_CIPHER structure
 #
 # returns: (string) cipher name e.g. 'DHE-RSA-AES256-SHA'

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CIPHER_get_name.html|http://www.openssl.org/docs/ssl/SSL_CIPHER_get_name.html>

Example:

 my $ssl_cipher = Net::SSLeay::get_current_cipher($ssl);
 my $cipher_name = Net::SSLeay::CIPHER_get_name($ssl_cipher);

=item * CIPHER_description

Returns a textual description of the cipher used.

??? (does this function really work?)

 my $rv = Net::SSLeay::CIPHER_description($cipher, $buf, $size);
 # $cipher - value corresponding to openssl's SSL_CIPHER structure
 # $bufer - (string/buffer) ???
 # $size - (integer) ???
 #
 # returns: (string) cipher description e.g. 'DHE-RSA-AES256-SHA SSLv3 Kx=DH Au=RSA Enc=AES(256) Mac=SHA1'

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CIPHER_get_name.html|http://www.openssl.org/docs/ssl/SSL_CIPHER_get_name.html>

=item * CIPHER_get_bits

Returns the number of secret bits used for cipher.

 my $rv = Net::SSLeay::CIPHER_get_bits($c);
 # $c - value corresponding to openssl's SSL_CIPHER structure
 #
 # returns: (integert) number of secret bits, 0 on error


Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_CIPHER_get_name.html|http://www.openssl.org/docs/ssl/SSL_CIPHER_get_name.html>

=back

=head3 Low level API: RSA_* related functions

=over

=item * RSA_generate_key

Generates a key pair and returns it in a newly allocated RSA structure.
The pseudo-random number generator must be seeded prior to calling RSA_generate_key.

 my $rv = Net::SSLeay::RSA_generate_key($bits, $e, $perl_cb, $perl_cb_arg);
 # $bits - (integer) modulus size in bits e.g. 512, 1024, 2048
 # $e - (integer) public exponent, an odd number, typically 3, 17 or 65537
 # $perl_cb - [optional] reference to perl callback function
 # $perl_cb_arg - [optional] data that will be passed to callback function when invoked
 #
 # returns: value corresponding to openssl's RSA structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/crypto/RSA_generate_key.html|http://www.openssl.org/docs/crypto/RSA_generate_key.html>

=item * RSA_free

Frees the RSA structure and its components. The key is erased before the memory is returned to the system.

 Net::SSLeay::RSA_free($r);
 # $r - value corresponding to openssl's RSA structure
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/crypto/RSA_new.html|http://www.openssl.org/docs/crypto/RSA_new.html>

=item * RSA_get_key_parameters

Returns a list of pointers to BIGNUMs representing the parameters of the key in
this order:
(n, e, d, p, q, dmp1, dmq1, iqmp)
Caution: returned list consists of SV pointers to BIGNUMs, which would need to be blessed as Crypt::OpenSSL::Bignum for further use

my (@params) = RSA_get_key_parameters($r);

=back

=head3 Low level API: BIO_* related functions

=over

=item * BIO_eof

Returns 1 if the BIO has read EOF, the precise meaning of 'EOF' varies according to the BIO type.

 my $rv = Net::SSLeay::BIO_eof($s);
 # $s - value corresponding to openssl's BIO structure
 #
 # returns: 1 if EOF has been reached 0 otherwise

Check openssl doc L<http://www.openssl.org/docs/crypto/BIO_ctrl.html|http://www.openssl.org/docs/crypto/BIO_ctrl.html>

=item * BIO_f_ssl

Returns the SSL BIO method. This is a filter BIO which is a wrapper
round the OpenSSL SSL routines adding a BIO 'flavour' to SSL I/O.

 my $rv = Net::SSLeay::BIO_f_ssl();
 #
 # returns: value corresponding to openssl's BIO_METHOD structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/crypto/BIO_f_ssl.html|http://www.openssl.org/docs/crypto/BIO_f_ssl.html>

=item * BIO_free

Frees up a single BIO.

 my $rv = Net::SSLeay::BIO_free($bio;);
 # $bio; - value corresponding to openssl's BIO structure
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/crypto/BIO_new.html|http://www.openssl.org/docs/crypto/BIO_new.html>

=item * BIO_new

Returns a new BIO using method $type

 my $rv = Net::SSLeay::BIO_new($type);
 # $type - value corresponding to openssl's BIO_METHOD structure
 #
 # returns: value corresponding to openssl's BIO structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/crypto/BIO_new.html|http://www.openssl.org/docs/crypto/BIO_new.html>

=item * BIO_new_buffer_ssl_connect

Creates a new BIO chain consisting of a buffering BIO, an SSL BIO (using ctx) and a connect BIO.

 my $rv = Net::SSLeay::BIO_new_buffer_ssl_connect($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: value corresponding to openssl's BIO structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/crypto/BIO_f_ssl.html|http://www.openssl.org/docs/crypto/BIO_f_ssl.html>

=item * BIO_new_file

Creates a new file BIO with mode $mode the meaning of mode is the same
as the stdio function fopen(). The BIO_CLOSE flag is set on the returned BIO.

 my $rv = Net::SSLeay::BIO_new_file($filename, $mode);
 # $filename - (string) filename
 # $mode - (string) opening mode (as mode by stdio function fopen)
 #
 # returns: value corresponding to openssl's BIO structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/crypto/BIO_s_file.html|http://www.openssl.org/docs/crypto/BIO_s_file.html>

=item * BIO_new_ssl

Allocates an SSL BIO using SSL_CTX ctx and using client mode if client is non zero.

 my $rv = Net::SSLeay::BIO_new_ssl($ctx, $client);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $client - (integer) 0 or 1 - indicates ssl client mode
 #
 # returns: value corresponding to openssl's BIO structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/crypto/BIO_f_ssl.html|http://www.openssl.org/docs/crypto/BIO_f_ssl.html>

=item * BIO_new_ssl_connect

Creates a new BIO chain consisting of an SSL BIO (using ctx) followed by a connect BIO.

 my $rv = Net::SSLeay::BIO_new_ssl_connect($ctx);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 #
 # returns: value corresponding to openssl's BIO structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/crypto/BIO_f_ssl.html|http://www.openssl.org/docs/crypto/BIO_f_ssl.html>

=item * BIO_pending

Return the number of pending characters in the BIOs read buffers.

 my $rv = Net::SSLeay::BIO_pending($s);
 # $s - value corresponding to openssl's BIO structure
 #
 # returns: the amount of pending data

Check openssl doc L<http://www.openssl.org/docs/crypto/BIO_ctrl.html|http://www.openssl.org/docs/crypto/BIO_ctrl.html>

=item * BIO_wpending

Return the number of pending characters in the BIOs write buffers.

 my $rv = Net::SSLeay::BIO_wpending($s);
 # $s - value corresponding to openssl's BIO structure
 #
 # returns: the amount of pending data

Check openssl doc L<http://www.openssl.org/docs/crypto/BIO_ctrl.html|http://www.openssl.org/docs/crypto/BIO_ctrl.html>

=item * BIO_read

Read the underlying descriptor.

 Net::SSLeay::BIO_read($s, $max);
 # $s - value corresponding to openssl's BIO structure
 # $max - [optional] max. bytes to read (if not specified, the value 32768 is used)
 #
 # returns: data

Check openssl doc L<http://www.openssl.org/docs/crypto/BIO_read.html|http://www.openssl.org/docs/crypto/BIO_read.html>

=item * BIO_write

Attempts to write data from $buffer to BIO $b.

 my $rv = Net::SSLeay::BIO_write($b, $buffer);
 # $b - value corresponding to openssl's BIO structure
 # $buffer - data
 #
 # returns: amount of data successfully written
 #          or that no data was successfully read or written if the result is 0 or -1
 #          or -2 when the operation is not implemented in the specific BIO type

Check openssl doc L<http://www.openssl.org/docs/crypto/BIO_read.html|http://www.openssl.org/docs/crypto/BIO_read.html>

=item * BIO_s_mem

Return the memory BIO method function.

 my $rv = Net::SSLeay::BIO_s_mem();
 #
 # returns: value corresponding to openssl's BIO_METHOD structure (0 on failure)

Check openssl doc L<http://www.openssl.org/docs/crypto/BIO_s_mem.html|http://www.openssl.org/docs/crypto/BIO_s_mem.html>

=item * BIO_ssl_copy_session_id

Copies an SSL session id between BIO chains from and to. It does this by locating
the SSL BIOs in each chain and calling SSL_copy_session_id() on the internal SSL pointer.

 my $rv = Net::SSLeay::BIO_ssl_copy_session_id($to, $from);
 # $to - value corresponding to openssl's BIO structure
 # $from - value corresponding to openssl's BIO structure
 #
 # returns: 1 on success, 0 on failure

Check openssl doc L<http://www.openssl.org/docs/crypto/BIO_f_ssl.html|http://www.openssl.org/docs/crypto/BIO_f_ssl.html>

=item * BIO_ssl_shutdown

Closes down an SSL connection on BIO chain bio. It does this by locating the
SSL BIO in the chain and calling SSL_shutdown() on its internal SSL pointer.

 Net::SSLeay::BIO_ssl_shutdown($ssl_bio);
 # $ssl_bio - value corresponding to openssl's BIO structure
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/crypto/BIO_f_ssl.html|http://www.openssl.org/docs/crypto/BIO_f_ssl.html>

=back

=head3 Low level API: Server side Server Name Indication (SNI) support

=over

=item * set_tlsext_host_name

TBA

=item * get_servername

TBA

=item * get_servername_type

TBA

=item * CTX_set_tlsext_servername_callback

B<COMPATIBILITY:> requires at least OpenSSL 0.9.8f

This function is used in a server to support Server side Server Name Indication (SNI).

 Net::SSLeay::CTX_set_tlsext_servername_callback($ctx, $code)
 # $ctx - SSL context
 # $code - reference to a subroutine that will be called when a new connection is being initiated
 #
 # returns: no return value
On the client side:
use set_tlsext_host_name($ssl, $servername) before initiating the SSL connection.

On the server side:
Set up an additional SSL_CTX() for each different certificate;

Add a servername callback to each SSL_CTX() using CTX_set_tlsext_servername_callback();

The callback function is required to retrieve the client-supplied servername
with get_servername(ssl). Figure out the right
SSL_CTX to go with that host name, then switch the SSL object to that SSL_CTX
with set_SSL_CTX().

Example:

 # set callback
 Net::SSLeay::CTX_set_tlsext_servername_callback($ctx, 
    sub {
      my $ssl = shift;
      my $h = Net::SSLeay::get_servername($ssl);
      Net::SSLeay::set_SSL_CTX($ssl, $hostnames{$h}->{ctx}) if exists $hostnames{$h};
    } );


More complete example:

 # ... initialize Net::SSLeay

 my %hostnames = (
   'sni1' => { cert=>'sni1.pem', key=>'sni1.key' },
   'sni2' => { cert=>'sni2.pem', key=>'sni2.key' },
 );

 # create a new context for each certificate/key pair
 for my $name (keys %hostnames) {
   $hostnames{$name}->{ctx} = Net::SSLeay::CTX_new or die;
   Net::SSLeay::CTX_set_cipher_list($hostnames{$name}->{ctx}, 'ALL');
   Net::SSLeay::set_cert_and_key($hostnames{$name}->{ctx},
   $hostnames{$name}->{cert}, $hostnames{$name}->{key}) or die;
 }

 # create default context
 my $ctx = Net::SSLeay::CTX_new or die;
 Net::SSLeay::CTX_set_cipher_list($ctx, 'ALL');
 Net::SSLeay::set_cert_and_key($ctx, 'cert.pem','key.pem') or die;

 # set callback
 Net::SSLeay::CTX_set_tlsext_servername_callback($ctx, sub {
   my $ssl = shift;
   my $h = Net::SSLeay::get_servername($ssl);
   Net::SSLeay::set_SSL_CTX($ssl, $hostnames{$h}->{ctx}) if exists $hostnames{$h};
   } );

 # ... later

 $s = Net::SSLeay::new($ctx);
 Net::SSLeay::set_fd($s, fileno($accepted_socket));
 Net::SSLeay::accept($s); 

=back 

=head3 Low level API: NPN (next protocol negotiation) related functions

NPN is being replaced with ALPN, a more recent TLS extension for application
protocol negotiation that's in process of being adopted by IETF. Please look
below for APLN API description.

Simple approach for using NPN support looks like this:

 ### client side
 use Net::SSLeay;
 use IO::Socket::INET;

 Net::SSLeay::initialize();
 my $sock = IO::Socket::INET->new(PeerAddr=>'encrypted.google.com:443') or die;
 my $ctx = Net::SSLeay::CTX_tlsv1_new() or die;
 Net::SSLeay::CTX_set_options($ctx, &Net::SSLeay::OP_ALL);
 Net::SSLeay::CTX_set_next_proto_select_cb($ctx, ['http1.1','spdy/2']);
 my $ssl = Net::SSLeay::new($ctx) or die;
 Net::SSLeay::set_fd($ssl, fileno($sock)) or die;
 Net::SSLeay::connect($ssl);

 warn "client:negotiated=",Net::SSLeay::P_next_proto_negotiated($ssl), "\n";
 warn "client:last_status=", Net::SSLeay::P_next_proto_last_status($ssl), "\n";
 
 ### server side 
 use Net::SSLeay;
 use IO::Socket::INET;
 
 Net::SSLeay::initialize();
 my $ctx = Net::SSLeay::CTX_tlsv1_new() or die;
 Net::SSLeay::CTX_set_options($ctx, &Net::SSLeay::OP_ALL);
 Net::SSLeay::set_cert_and_key($ctx, "cert.pem", "key.pem");
 Net::SSLeay::CTX_set_next_protos_advertised_cb($ctx, ['spdy/2','http1.1']);
 my $sock = IO::Socket::INET->new(LocalAddr=>'localhost', LocalPort=>5443, Proto=>'tcp', Listen=>20) or die;
 
 while (1) {
   my $ssl = Net::SSLeay::new($ctx);
   warn("server:waiting for incoming connection...\n");
   my $fd = $sock->accept();
   Net::SSLeay::set_fd($ssl, $fd->fileno);
   Net::SSLeay::accept($ssl);  
   warn "server:negotiated=",Net::SSLeay::P_next_proto_negotiated($ssl),"\n";
   my $got = Net::SSLeay::read($ssl);
   Net::SSLeay::ssl_write_all($ssl, "length=".length($got));
   Net::SSLeay::free($ssl);
   $fd->close();
 }
 # check with: openssl s_client -connect localhost:5443 -nextprotoneg http/1.1,spdy/2

Please note that the selection (negotiation) is performed by client side, the server side simply advertise the list of supported protocols.

Advanced approach allows you to implement your own negotiation algorithm.

 #see below documentation for:
 Net::SSleay::CTX_set_next_proto_select_cb($ctx, $perl_callback_function, $callback_data);
 Net::SSleay::CTX_set_next_protos_advertised_cb($ctx, $perl_callback_function, $callback_data);

Detection of NPN support (works even in older Net::SSLeay versions):

 use Net::SSLeay;
 
 if (exists &Net::SSLeay::P_next_proto_negotiated) {
   # do NPN stuff
 }

=over

=item * CTX_set_next_proto_select_cb

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before; requires at least openssl-1.0.1

B<NOTE:> You need CTX_set_next_proto_select_cb on B<client side> of SSL connection.

Simple usage - in this case a "common" negotiation algorithm (as implemented by openssl's function SSL_select_next_proto) is used.

 $rv = Net::SSleay::CTX_set_next_proto_select_cb($ctx, $arrayref);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $arrayref - list of accepted protocols - e.g. ['http1.0', 'http1.1']
 #
 # returns: 0 on success, 1 on failure

Advanced usage (you probably do not need this):
 
 $rv = Net::SSleay::CTX_set_next_proto_select_cb($ctx, $perl_callback_function, $callback_data);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $perl_callback_function - reference to perl function
 # $callback_data - [optional] data to passed to callback function when invoked
 #
 # returns: 0 on success, 1 on failure
 
 # where callback function looks like
 sub npn_advertised_cb_invoke {
   my ($ssl, $arrayref_proto_list_advertised_by_server, $callback_data) = @_;
   my $status;
   # ...
   $status = 1;   #status can be:
                  # 0 - OPENSSL_NPN_UNSUPPORTED
                  # 1 - OPENSSL_NPN_NEGOTIATED
                  # 2 - OPENSSL_NPN_NO_OVERLAP
   return $status, ['http1.1','spdy/2']; # the callback has to return 2 values
 }

To undefine/clear this callback use:

 Net::SSleay::CTX_set_next_proto_select_cb($ctx, undef);

=item * CTX_set_next_protos_advertised_cb

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before; requires at least openssl-1.0.1

B<NOTE:> You need CTX_set_next_proto_select_cb on B<server side> of SSL connection.

Simple usage:

 $rv = Net::SSleay::CTX_set_next_protos_advertised_cb($ctx, $arrayref);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $arrayref - list of advertised protocols - e.g. ['http1.0', 'http1.1']
 #
 # returns: 0 on success, 1 on failure

Advanced usage (you probably do not need this):
 
 $rv = Net::SSleay::CTX_set_next_protos_advertised_cb($ctx, $perl_callback_function, $callback_data);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $perl_callback_function - reference to perl function
 # $callback_data - [optional] data to passed to callback function when invoked
 #
 # returns: 0 on success, 1 on failure
 
 # where callback function looks like
 sub npn_advertised_cb_invoke {
   my ($ssl, $callback_data) = @_;
   # ...
   return ['http1.1','spdy/2']; # the callback has to return arrayref
 }

To undefine/clear this callback use:

 Net::SSleay::CTX_set_next_protos_advertised_cb($ctx, undef);

=item * P_next_proto_negotiated

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before; requires at least openssl-1.0.1

Returns the name of negotiated protocol for given SSL connection $ssl.

 $rv = Net::SSLeay::P_next_proto_negotiated($ssl)
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: (string) negotiated protocol name (or undef if no negotiation was done or failed with fatal error)

=item * P_next_proto_last_status

B<COMPATIBILITY:> not available in Net-SSLeay-1.45 and before; requires at least openssl-1.0.1

Returns the result of the last negotiation for given SSL connection $ssl.

 $rv = Net::SSLeay::P_next_proto_last_status($ssl)
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: (integer) negotiation status
 #          0 - OPENSSL_NPN_UNSUPPORTED
 #          1 - OPENSSL_NPN_NEGOTIATED
 #          2 - OPENSSL_NPN_NO_OVERLAP

=back

=head3 Low level API: ALPN (application layer protocol negotiation) related functions

Application protocol can be negotiated via two different mechanisms employing
two different TLS extensions: NPN (obsolete) and ALPN (recommended).

The API is rather similar, with slight differences reflecting protocol
specifics. In particular, with ALPN the protocol negotiation takes place on
server, while with NPN the client implements the protocol negotiation logic.

With ALPN, the most basic implementation looks like this:

 ### client side
 use Net::SSLeay;
 use IO::Socket::INET;

 Net::SSLeay::initialize();
 my $sock = IO::Socket::INET->new(PeerAddr=>'encrypted.google.com:443') or die;
 my $ctx = Net::SSLeay::CTX_tlsv1_new() or die;
 Net::SSLeay::CTX_set_options($ctx, &Net::SSLeay::OP_ALL);
 Net::SSLeay::CTX_set_alpn_protos($ctx, ['http/1.1', 'http/2.0', 'spdy/3]);
 my $ssl = Net::SSLeay::new($ctx) or die;
 Net::SSLeay::set_fd($ssl, fileno($sock)) or die;
 Net::SSLeay::connect($ssl);

 warn "client:selected=",Net::SSLeay::P_alpn_selected($ssl), "\n";

 ### server side
 use Net::SSLeay;
 use IO::Socket::INET;

 Net::SSLeay::initialize();
 my $ctx = Net::SSLeay::CTX_tlsv1_new() or die;
 Net::SSLeay::CTX_set_options($ctx, &Net::SSLeay::OP_ALL);
 Net::SSLeay::set_cert_and_key($ctx, "cert.pem", "key.pem");
 Net::SSLeay::CTX_set_alpn_select_cb($ctx, ['http/1.1', 'http/2.0', 'spdy/3]);
 my $sock = IO::Socket::INET->new(LocalAddr=>'localhost', LocalPort=>5443, Proto=>'tcp', Listen=>20) or die;

 while (1) {
   my $ssl = Net::SSLeay::new($ctx);
   warn("server:waiting for incoming connection...\n");
   my $fd = $sock->accept();
   Net::SSLeay::set_fd($ssl, $fd->fileno);
   Net::SSLeay::accept($ssl);
   warn "server:selected=",Net::SSLeay::P_alpn_selected($ssl),"\n";
   my $got = Net::SSLeay::read($ssl);
   Net::SSLeay::ssl_write_all($ssl, "length=".length($got));
   Net::SSLeay::free($ssl);
   $fd->close();
 }
 # check with: openssl s_client -connect localhost:5443 -alpn spdy/3,http/1.1

Advanced approach allows you to implement your own negotiation algorithm.

 #see below documentation for:
 Net::SSleay::CTX_set_alpn_select_cb($ctx, $perl_callback_function, $callback_data);

Detection of ALPN support (works even in older Net::SSLeay versions):

 use Net::SSLeay;

 if (exists &Net::SSLeay::P_alpn_selected) {
   # do ALPN stuff
 }

=over

=item * CTX_set_alpn_select_cb

B<COMPATIBILITY:> not available in Net-SSLeay-1.55 and before; requires at least openssl-1.0.2

B<NOTE:> You need CTX_set_alpn_select_cb on B<server side> of TLS connection.

Simple usage - in this case a "common" negotiation algorithm (as implemented by openssl's function SSL_select_next_proto) is used.

 $rv = Net::SSleay::CTX_set_alpn_select_cb($ctx, $arrayref);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $arrayref - list of accepted protocols - e.g. ['http/2.0', 'http/1.1', 'spdy/3']
 #
 # returns: 0 on success, 1 on failure

Advanced usage (you probably do not need this):

 $rv = Net::SSleay::CTX_set_alpn_select_cb($ctx, $perl_callback_function, $callback_data);
 # $ctx - value corresponding to openssl's SSL_CTX structure
 # $perl_callback_function - reference to perl function
 # $callback_data - [optional] data to passed to callback function when invoked
 #
 # returns: 0 on success, 1 on failure

 # where callback function looks like
 sub alpn_select_cb_invoke {
   my ($ssl, $arrayref_proto_list_advertised_by_client, $callback_data) = @_;
   # ...
   if ($negotiated) {
     return 'http/2.0';
   } else {
     return undef;
   }
 }

To undefine/clear this callback use:

 Net::SSleay::CTX_set_alpn_select_cb($ctx, undef);

=item * set_alpn_protos

B<COMPATIBILITY:> not available in Net-SSLeay-1.55 and before; requires at least openssl-1.0.2

B<NOTE:> You need set_alpn_protos on B<client side> of TLS connection.

This adds list of supported application layer protocols to ClientHello message sent by a client.
It advertises the enumeration of supported protocols:

 Net::SSLeay::set_alpn_protos($ssl, ['http/1.1', 'http/2.0', 'spdy/3]);
 # returns 0 on success

=item * CTX_set_alpn_protos

B<COMPATIBILITY:> not available in Net-SSLeay-1.55 and before; requires at least openssl-1.0.2

B<NOTE:> You need CTX_set_alpn_protos on B<client side> of TLS connection.

This adds list of supported application layer protocols to ClientHello message sent by a client.
It advertises the enumeration of supported protocols:

 Net::SSLeay::CTX_set_alpn_protos($ctx, ['http/1.1', 'http/2.0', 'spdy/3]);
 # returns 0 on success

=item * P_alpn_selected

B<COMPATIBILITY:> not available in Net-SSLeay-1.55 and before; requires at least openssl-1.0.2

Returns the name of negotiated protocol for given TLS connection $ssl.

 $rv = Net::SSLeay::P_alpn_selected($ssl)
 # $ssl - value corresponding to openssl's SSL structure
 #
 # returns: (string) negotiated protocol name (or undef if no negotiation was done or failed with fatal error)

=back

=head3 Low level API: DANE Support

OpenSSL version 1.0.2 adds preliminary support RFC6698 Domain Authentication of
Named Entities (DANE) Transport Layer Association within OpenSSL

=over 

=item * SSL_get_tlsa_record_byname

B<COMPATIBILITY:> DELETED from net-ssleay, since it is not supported by OpenSSL

In order to facilitate DANE there is additional interface,
SSL_get_tlsa_record_byname, accepting hostname, port and socket type
that returns packed TLSA record. In order to make it even easier there
is additional SSL_ctrl function that calls SSL_get_tlsa_record_byname
for you. Latter is recommended for programmers that wish to maintain
broader binary compatibility, e.g. make application work with both 1.0.2
and prior version (in which case call to SSL_ctrl with new code
returning error would have to be ignored when running with prior version).

Net::SSLeay::get_tlsa_record_byname($name, $port, $type);

=back

=head3 Low level API: Other functions

=over

=item * COMP_add_compression_method

Adds the compression method cm with the identifier id to the list of available compression methods.
This list is globally maintained for all SSL operations within this application.
It cannot be set for specific SSL_CTX or SSL objects.

 my $rv = Net::SSLeay::COMP_add_compression_method($id, $cm);
 # $id - (integer) compression method id
 #       0 to 63:    methods defined by the IETF
 #       64 to 192:  external party methods assigned by IANA
 #       193 to 255: reserved for private use
 #
 # $cm - value corresponding to openssl's COMP_METHOD structure
 #
 # returns: 0 on success, 1 on failure (check the error queue to find out the reason)

Check openssl doc L<http://www.openssl.org/docs/ssl/SSL_COMP_add_compression_method.html|http://www.openssl.org/docs/ssl/SSL_COMP_add_compression_method.html>

=item * DH_free

Frees the DH structure and its components. The values are erased before the memory is returned to the system.

 Net::SSLeay::DH_free($dh);
 # $dh - value corresponding to openssl's DH structure
 #
 # returns: no return value

Check openssl doc L<http://www.openssl.org/docs/crypto/DH_new.html|http://www.openssl.org/docs/crypto/DH_new.html>

=item * FIPS_mode_set

Enable or disable FIPS mode in a FIPS capable OpenSSL.

 Net::SSLeay:: FIPS_mode_set($enable);
 # $enable - (integer) 1 to enable, 0 to disable

=back

=head3 Low level API: EC related functions

=over 

=item * CTX_set_tmp_ecdh

TBA

=item * EC_KEY_free

TBA

=item * EC_KEY_new_by_curve_name

TBA

=item * EC_KEY_generate_key

Generates a EC key and returns it in a newly allocated EC_KEY structure.
The EC key then can be used to create a PKEY which can be used in calls
like X509_set_pubkey.

 my $key = Net::SSLeay::EVP_PKEY_new();
 my $ec  = Net::SSLeay::EC_KEY_generate_key($curve);
 Net::SSLeay::EVP_PKEY_assign_EC_KEY($key,$ec);

 # $curve - curve name like 'secp521r1' or the matching Id (integer) of the curve
 #
 # returns: value corresponding to openssl's EC_KEY structure (0 on failure)

This function has no equivalent in OpenSSL but combines multiple OpenSSL
functions for an easier interface.

=item * CTX_set_ecdh_auto, set_ecdh_auto

These functions enable or disable the automatic curve selection on the server
side by calling SSL_CTX_set_ecdh_auto or SSL_set_ecdh_auto respectively.
If enabled the highest preference curve is automatically used for ECDH temporary
keys used during key exchange.
This function is no longer available for OpenSSL 1.1.0 or higher.

  Net::SSLeay::CTX_set_ecdh_auto($ctx,1);
  Net::SSLeay::set_ecdh_auto($ssl,1);

=item * CTX_set1_curves_list, set1_curves_list

These functions set the supported curves (in order of preference) by calling
SSL_CTX_set1_curves_list or SSL_set1_curves_list respectively.
For a TLS client these curves are offered to the server in the supported curves
extension while on the server side these are used to determine the shared
curve.
These functions are only available since OpenSSL 1.1.0.

  Net::SSLeay::CTX_set1_curves_list($ctx,"P-521:P-384:P-256");
  Net::SSLeay::set1_curves_list($ssl,"P-521:P-384:P-256");

=item * CTX_set1_groups_list, set1_groups_list

These functions set the supported groups (in order of preference) by calling
SSL_CTX_set1_groups_list or SSL_set1_groups_list respectively.
This is practically the same as CTX_set1_curves_list and set1_curves_list except
that all DH groups can be given as supported by TLS 1.3.
These functions are only available since OpenSSL 1.1.1.

  Net::SSLeay::CTX_set1_groups_list($ctx,"P-521:P-384:P-256");
  Net::SSLeay::set1_groups_list($ssl,"P-521:P-384:P-256");

=back


=head2 Constants

There are many openssl constants available in L<Net::SSLeay>. You can use them like this:

 use Net::SSLeay;
 print &Net::SSLeay::NID_commonName;
 #or
 print Net::SSLeay::NID_commonName();

Or you can import them and use:

 use Net::SSLeay qw/NID_commonName/;
 print &NID_commonName;
 #or
 print NID_commonName();
 #or
 print NID_commonName;

The constants names are derived from openssl constants, however constants starting with C<SSL_> prefix
have name with C<SSL_> part stripped - e.g. openssl's constant C<SSL_OP_ALL> is available as C<Net::SSleay::OP_ALL>

The list of all available constant names:

=for comment the next part is the output of: perl helper_script/regen_openssl_constants.pl -gen-pod

 ASN1_STRFLGS_ESC_CTRL           NID_netscape                              R_UNKNOWN_REMOTE_ERROR_TYPE
 ASN1_STRFLGS_ESC_MSB            NID_netscape_base_url                     R_UNKNOWN_STATE
 ASN1_STRFLGS_ESC_QUOTE          NID_netscape_ca_policy_url                R_X509_LIB
 ASN1_STRFLGS_RFC2253            NID_netscape_ca_revocation_url            SENT_SHUTDOWN
 CB_ACCEPT_EXIT                  NID_netscape_cert_extension               SESSION_ASN1_VERSION
 CB_ACCEPT_LOOP                  NID_netscape_cert_sequence                SESS_CACHE_BOTH
 CB_ALERT                        NID_netscape_cert_type                    SESS_CACHE_CLIENT
 CB_CONNECT_EXIT                 NID_netscape_comment                      SESS_CACHE_NO_AUTO_CLEAR
 CB_CONNECT_LOOP                 NID_netscape_data_type                    SESS_CACHE_NO_INTERNAL
 CB_EXIT                         NID_netscape_renewal_url                  SESS_CACHE_NO_INTERNAL_LOOKUP
 CB_HANDSHAKE_DONE               NID_netscape_revocation_url               SESS_CACHE_NO_INTERNAL_STORE
 CB_HANDSHAKE_START              NID_netscape_ssl_server_name              SESS_CACHE_OFF
 CB_LOOP                         NID_ns_sgc                                SESS_CACHE_SERVER
 CB_READ                         NID_organizationName                      SSL3_VERSION
 CB_READ_ALERT                   NID_organizationalUnitName                SSLEAY_BUILT_ON
 CB_WRITE                        NID_pbeWithMD2AndDES_CBC                  SSLEAY_CFLAGS
 CB_WRITE_ALERT                  NID_pbeWithMD2AndRC2_CBC                  SSLEAY_DIR
 ERROR_NONE                      NID_pbeWithMD5AndCast5_CBC                SSLEAY_PLATFORM
 ERROR_SSL                       NID_pbeWithMD5AndDES_CBC                  SSLEAY_VERSION
 ERROR_SYSCALL                   NID_pbeWithMD5AndRC2_CBC                  ST_ACCEPT
 ERROR_WANT_ACCEPT               NID_pbeWithSHA1AndDES_CBC                 ST_BEFORE
 ERROR_WANT_CONNECT              NID_pbeWithSHA1AndRC2_CBC                 ST_CONNECT
 ERROR_WANT_READ                 NID_pbe_WithSHA1And128BitRC2_CBC          ST_INIT
 ERROR_WANT_WRITE                NID_pbe_WithSHA1And128BitRC4              ST_OK
 ERROR_WANT_X509_LOOKUP          NID_pbe_WithSHA1And2_Key_TripleDES_CBC    ST_READ_BODY
 ERROR_ZERO_RETURN               NID_pbe_WithSHA1And3_Key_TripleDES_CBC    ST_READ_HEADER
 EVP_PKS_DSA                     NID_pbe_WithSHA1And40BitRC2_CBC           TLS1_1_VERSION
 EVP_PKS_EC                      NID_pbe_WithSHA1And40BitRC4               TLS1_2_VERSION
 EVP_PKS_RSA                     NID_pbes2                                 TLS1_3_VERSION
 EVP_PKT_ENC                     NID_pbmac1                                TLS1_VERSION
 EVP_PKT_EXCH                    NID_pkcs                                  TLSEXT_STATUSTYPE_ocsp
 EVP_PKT_EXP                     NID_pkcs3                                 VERIFY_CLIENT_ONCE
 EVP_PKT_SIGN                    NID_pkcs7                                 VERIFY_FAIL_IF_NO_PEER_CERT
 EVP_PK_DH                       NID_pkcs7_data                            VERIFY_NONE
 EVP_PK_DSA                      NID_pkcs7_digest                          VERIFY_PEER
 EVP_PK_EC                       NID_pkcs7_encrypted                       VERIFY_POST_HANDSHAKE
 EVP_PK_RSA                      NID_pkcs7_enveloped                       V_OCSP_CERTSTATUS_GOOD
 FILETYPE_ASN1                   NID_pkcs7_signed                          V_OCSP_CERTSTATUS_REVOKED
 FILETYPE_PEM                    NID_pkcs7_signedAndEnveloped              V_OCSP_CERTSTATUS_UNKNOWN
 F_CLIENT_CERTIFICATE            NID_pkcs8ShroudedKeyBag                   WRITING
 F_CLIENT_HELLO                  NID_pkcs9                                 X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT
 F_CLIENT_MASTER_KEY             NID_pkcs9_challengePassword               X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS
 F_D2I_SSL_SESSION               NID_pkcs9_contentType                     X509_CHECK_FLAG_NEVER_CHECK_SUBJECT
 F_GET_CLIENT_FINISHED           NID_pkcs9_countersignature                X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS
 F_GET_CLIENT_HELLO              NID_pkcs9_emailAddress                    X509_CHECK_FLAG_NO_WILDCARDS
 F_GET_CLIENT_MASTER_KEY         NID_pkcs9_extCertAttributes               X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS
 F_GET_SERVER_FINISHED           NID_pkcs9_messageDigest                   X509_FILETYPE_ASN1
 F_GET_SERVER_HELLO              NID_pkcs9_signingTime                     X509_FILETYPE_DEFAULT
 F_GET_SERVER_VERIFY             NID_pkcs9_unstructuredAddress             X509_FILETYPE_PEM
 F_I2D_SSL_SESSION               NID_pkcs9_unstructuredName                X509_LOOKUP
 F_READ_N                        NID_private_key_usage_period              X509_PURPOSE_ANY
 F_REQUEST_CERTIFICATE           NID_rc2_40_cbc                            X509_PURPOSE_CRL_SIGN
 F_SERVER_HELLO                  NID_rc2_64_cbc                            X509_PURPOSE_NS_SSL_SERVER
 F_SSL_CERT_NEW                  NID_rc2_cbc                               X509_PURPOSE_OCSP_HELPER
 F_SSL_GET_NEW_SESSION           NID_rc2_cfb64                             X509_PURPOSE_SMIME_ENCRYPT
 F_SSL_NEW                       NID_rc2_ecb                               X509_PURPOSE_SMIME_SIGN
 F_SSL_READ                      NID_rc2_ofb64                             X509_PURPOSE_SSL_CLIENT
 F_SSL_RSA_PRIVATE_DECRYPT       NID_rc4                                   X509_PURPOSE_SSL_SERVER
 F_SSL_RSA_PUBLIC_ENCRYPT        NID_rc4_40                                X509_PURPOSE_TIMESTAMP_SIGN
 F_SSL_SESSION_NEW               NID_rc5_cbc                               X509_TRUST_COMPAT
 F_SSL_SESSION_PRINT_FP          NID_rc5_cfb64                             X509_TRUST_EMAIL
 F_SSL_SET_FD                    NID_rc5_ecb                               X509_TRUST_OBJECT_SIGN
 F_SSL_SET_RFD                   NID_rc5_ofb64                             X509_TRUST_OCSP_REQUEST
 F_SSL_SET_WFD                   NID_ripemd160                             X509_TRUST_OCSP_SIGN
 F_SSL_USE_CERTIFICATE           NID_ripemd160WithRSA                      X509_TRUST_SSL_CLIENT
 F_SSL_USE_CERTIFICATE_ASN1      NID_rle_compression                       X509_TRUST_SSL_SERVER
 F_SSL_USE_CERTIFICATE_FILE      NID_rsa                                   X509_TRUST_TSA
 F_SSL_USE_PRIVATEKEY            NID_rsaEncryption                         X509_V_ERR_AKID_ISSUER_SERIAL_MISMATCH
 F_SSL_USE_PRIVATEKEY_ASN1       NID_rsadsi                                X509_V_ERR_AKID_SKID_MISMATCH
 F_SSL_USE_PRIVATEKEY_FILE       NID_safeContentsBag                       X509_V_ERR_APPLICATION_VERIFICATION
 F_SSL_USE_RSAPRIVATEKEY         NID_sdsiCertificate                       X509_V_ERR_CA_KEY_TOO_SMALL
 F_SSL_USE_RSAPRIVATEKEY_ASN1    NID_secretBag                             X509_V_ERR_CA_MD_TOO_WEAK
 F_SSL_USE_RSAPRIVATEKEY_FILE    NID_serialNumber                          X509_V_ERR_CERT_CHAIN_TOO_LONG
 F_WRITE_PENDING                 NID_server_auth                           X509_V_ERR_CERT_HAS_EXPIRED
 GEN_DIRNAME                     NID_sha                                   X509_V_ERR_CERT_NOT_YET_VALID
 GEN_DNS                         NID_sha1                                  X509_V_ERR_CERT_REJECTED
 GEN_EDIPARTY                    NID_sha1WithRSA                           X509_V_ERR_CERT_REVOKED
 GEN_EMAIL                       NID_sha1WithRSAEncryption                 X509_V_ERR_CERT_SIGNATURE_FAILURE
 GEN_IPADD                       NID_shaWithRSAEncryption                  X509_V_ERR_CERT_UNTRUSTED
 GEN_OTHERNAME                   NID_stateOrProvinceName                   X509_V_ERR_CRL_HAS_EXPIRED
 GEN_RID                         NID_subject_alt_name                      X509_V_ERR_CRL_NOT_YET_VALID
 GEN_URI                         NID_subject_key_identifier                X509_V_ERR_CRL_PATH_VALIDATION_ERROR
 GEN_X400                        NID_surname                               X509_V_ERR_CRL_SIGNATURE_FAILURE
 LIBRESSL_VERSION_NUMBER         NID_sxnet                                 X509_V_ERR_DANE_NO_MATCH
 MBSTRING_ASC                    NID_time_stamp                            X509_V_ERR_DEPTH_ZERO_SELF_SIGNED_CERT
 MBSTRING_BMP                    NID_title                                 X509_V_ERR_DIFFERENT_CRL_SCOPE
 MBSTRING_FLAG                   NID_undef                                 X509_V_ERR_EE_KEY_TOO_SMALL
 MBSTRING_UNIV                   NID_uniqueIdentifier                      X509_V_ERR_EMAIL_MISMATCH
 MBSTRING_UTF8                   NID_x509Certificate                       X509_V_ERR_ERROR_IN_CERT_NOT_AFTER_FIELD
 MIN_RSA_MODULUS_LENGTH_IN_BYTES NID_x509Crl                               X509_V_ERR_ERROR_IN_CERT_NOT_BEFORE_FIELD
 MODE_ACCEPT_MOVING_WRITE_BUFFER NID_zlib_compression                      X509_V_ERR_ERROR_IN_CRL_LAST_UPDATE_FIELD
 MODE_AUTO_RETRY                 NOTHING                                   X509_V_ERR_ERROR_IN_CRL_NEXT_UPDATE_FIELD
 MODE_ENABLE_PARTIAL_WRITE       OCSP_RESPONSE_STATUS_INTERNALERROR        X509_V_ERR_EXCLUDED_VIOLATION
 MODE_RELEASE_BUFFERS            OCSP_RESPONSE_STATUS_MALFORMEDREQUEST     X509_V_ERR_HOSTNAME_MISMATCH
 NID_OCSP_sign                   OCSP_RESPONSE_STATUS_SIGREQUIRED          X509_V_ERR_INVALID_CA
 NID_SMIMECapabilities           OCSP_RESPONSE_STATUS_SUCCESSFUL           X509_V_ERR_INVALID_CALL
 NID_X500                        OCSP_RESPONSE_STATUS_TRYLATER             X509_V_ERR_INVALID_EXTENSION
 NID_X509                        OCSP_RESPONSE_STATUS_UNAUTHORIZED         X509_V_ERR_INVALID_NON_CA
 NID_ad_OCSP                     OPENSSL_BUILT_ON                          X509_V_ERR_INVALID_POLICY_EXTENSION
 NID_ad_ca_issuers               OPENSSL_CFLAGS                            X509_V_ERR_INVALID_PURPOSE
 NID_algorithm                   OPENSSL_DIR                               X509_V_ERR_IP_ADDRESS_MISMATCH
 NID_authority_key_identifier    OPENSSL_ENGINES_DIR                       X509_V_ERR_KEYUSAGE_NO_CERTSIGN
 NID_basic_constraints           OPENSSL_PLATFORM                          X509_V_ERR_KEYUSAGE_NO_CRL_SIGN
 NID_bf_cbc                      OPENSSL_VERSION                           X509_V_ERR_KEYUSAGE_NO_DIGITAL_SIGNATURE
 NID_bf_cfb64                    OPENSSL_VERSION_NUMBER                    X509_V_ERR_NO_EXPLICIT_POLICY
 NID_bf_ecb                      OP_ALL                                    X509_V_ERR_NO_VALID_SCTS
 NID_bf_ofb64                    OP_ALLOW_NO_DHE_KEX                       X509_V_ERR_OCSP_CERT_UNKNOWN
 NID_cast5_cbc                   OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION      X509_V_ERR_OCSP_VERIFY_FAILED
 NID_cast5_cfb64                 OP_CIPHER_SERVER_PREFERENCE               X509_V_ERR_OCSP_VERIFY_NEEDED
 NID_cast5_ecb                   OP_CISCO_ANYCONNECT                       X509_V_ERR_OUT_OF_MEM
 NID_cast5_ofb64                 OP_COOKIE_EXCHANGE                        X509_V_ERR_PATH_LENGTH_EXCEEDED
 NID_certBag                     OP_CRYPTOPRO_TLSEXT_BUG                   X509_V_ERR_PATH_LOOP
 NID_certificate_policies        OP_DONT_INSERT_EMPTY_FRAGMENTS            X509_V_ERR_PERMITTED_VIOLATION
 NID_client_auth                 OP_ENABLE_MIDDLEBOX_COMPAT                X509_V_ERR_PROXY_CERTIFICATES_NOT_ALLOWED
 NID_code_sign                   OP_EPHEMERAL_RSA                          X509_V_ERR_PROXY_PATH_LENGTH_EXCEEDED
 NID_commonName                  OP_LEGACY_SERVER_CONNECT                  X509_V_ERR_PROXY_SUBJECT_NAME_VIOLATION
 NID_countryName                 OP_MICROSOFT_BIG_SSLV3_BUFFER             X509_V_ERR_SELF_SIGNED_CERT_IN_CHAIN
 NID_crlBag                      OP_MICROSOFT_SESS_ID_BUG                  X509_V_ERR_STORE_LOOKUP
 NID_crl_distribution_points     OP_MSIE_SSLV2_RSA_PADDING                 X509_V_ERR_SUBJECT_ISSUER_MISMATCH
 NID_crl_number                  OP_NETSCAPE_CA_DN_BUG                     X509_V_ERR_SUBTREE_MINMAX
 NID_crl_reason                  OP_NETSCAPE_CHALLENGE_BUG                 X509_V_ERR_SUITE_B_CANNOT_SIGN_P_384_WITH_P_256
 NID_delta_crl                   OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG        X509_V_ERR_SUITE_B_INVALID_ALGORITHM
 NID_des_cbc                     OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG       X509_V_ERR_SUITE_B_INVALID_CURVE
 NID_des_cfb64                   OP_NON_EXPORT_FIRST                       X509_V_ERR_SUITE_B_INVALID_SIGNATURE_ALGORITHM
 NID_des_ecb                     OP_NO_ANTI_REPLAY                         X509_V_ERR_SUITE_B_INVALID_VERSION
 NID_des_ede                     OP_NO_CLIENT_RENEGOTIATION                X509_V_ERR_SUITE_B_LOS_NOT_ALLOWED
 NID_des_ede3                    OP_NO_COMPRESSION                         X509_V_ERR_UNABLE_TO_DECODE_ISSUER_PUBLIC_KEY
 NID_des_ede3_cbc                OP_NO_ENCRYPT_THEN_MAC                    X509_V_ERR_UNABLE_TO_DECRYPT_CERT_SIGNATURE
 NID_des_ede3_cfb64              OP_NO_QUERY_MTU                           X509_V_ERR_UNABLE_TO_DECRYPT_CRL_SIGNATURE
 NID_des_ede3_ofb64              OP_NO_RENEGOTIATION                       X509_V_ERR_UNABLE_TO_GET_CRL
 NID_des_ede_cbc                 OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION X509_V_ERR_UNABLE_TO_GET_CRL_ISSUER
 NID_des_ede_cfb64               OP_NO_SSL_MASK                            X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT
 NID_des_ede_ofb64               OP_NO_SSLv2                               X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY
 NID_des_ofb64                   OP_NO_SSLv3                               X509_V_ERR_UNABLE_TO_VERIFY_LEAF_SIGNATURE
 NID_description                 OP_NO_TICKET                              X509_V_ERR_UNHANDLED_CRITICAL_CRL_EXTENSION
 NID_desx_cbc                    OP_NO_TLSv1                               X509_V_ERR_UNHANDLED_CRITICAL_EXTENSION
 NID_dhKeyAgreement              OP_NO_TLSv1_1                             X509_V_ERR_UNNESTED_RESOURCE
 NID_dnQualifier                 OP_NO_TLSv1_2                             X509_V_ERR_UNSPECIFIED
 NID_dsa                         OP_NO_TLSv1_3                             X509_V_ERR_UNSUPPORTED_CONSTRAINT_SYNTAX
 NID_dsaWithSHA                  OP_PKCS1_CHECK_1                          X509_V_ERR_UNSUPPORTED_CONSTRAINT_TYPE
 NID_dsaWithSHA1                 OP_PKCS1_CHECK_2                          X509_V_ERR_UNSUPPORTED_EXTENSION_FEATURE
 NID_dsaWithSHA1_2               OP_PRIORITIZE_CHACHA                      X509_V_ERR_UNSUPPORTED_NAME_SYNTAX
 NID_dsa_2                       OP_SAFARI_ECDHE_ECDSA_BUG                 X509_V_FLAG_ALLOW_PROXY_CERTS
 NID_email_protect               OP_SINGLE_DH_USE                          X509_V_FLAG_CB_ISSUER_CHECK
 NID_ext_key_usage               OP_SINGLE_ECDH_USE                        X509_V_FLAG_CHECK_SS_SIGNATURE
 NID_ext_req                     OP_SSLEAY_080_CLIENT_DH_BUG               X509_V_FLAG_CRL_CHECK
 NID_friendlyName                OP_SSLREF2_REUSE_CERT_TYPE_BUG            X509_V_FLAG_CRL_CHECK_ALL
 NID_givenName                   OP_TLSEXT_PADDING                         X509_V_FLAG_EXPLICIT_POLICY
 NID_hmacWithSHA1                OP_TLS_BLOCK_PADDING_BUG                  X509_V_FLAG_EXTENDED_CRL_SUPPORT
 NID_id_ad                       OP_TLS_D5_BUG                             X509_V_FLAG_IGNORE_CRITICAL
 NID_id_ce                       OP_TLS_ROLLBACK_BUG                       X509_V_FLAG_INHIBIT_ANY
 NID_id_kp                       READING                                   X509_V_FLAG_INHIBIT_MAP
 NID_id_pbkdf2                   RECEIVED_SHUTDOWN                         X509_V_FLAG_NOTIFY_POLICY
 NID_id_pe                       RSA_3                                     X509_V_FLAG_NO_ALT_CHAINS
 NID_id_pkix                     RSA_F4                                    X509_V_FLAG_NO_CHECK_TIME
 NID_id_qt_cps                   R_BAD_AUTHENTICATION_TYPE                 X509_V_FLAG_PARTIAL_CHAIN
 NID_id_qt_unotice               R_BAD_CHECKSUM                            X509_V_FLAG_POLICY_CHECK
 NID_idea_cbc                    R_BAD_MAC_DECODE                          X509_V_FLAG_POLICY_MASK
 NID_idea_cfb64                  R_BAD_RESPONSE_ARGUMENT                   X509_V_FLAG_SUITEB_128_LOS
 NID_idea_ecb                    R_BAD_SSL_FILETYPE                        X509_V_FLAG_SUITEB_128_LOS_ONLY
 NID_idea_ofb64                  R_BAD_SSL_SESSION_ID_LENGTH               X509_V_FLAG_SUITEB_192_LOS
 NID_info_access                 R_BAD_STATE                               X509_V_FLAG_TRUSTED_FIRST
 NID_initials                    R_BAD_WRITE_RETRY                         X509_V_FLAG_USE_CHECK_TIME
 NID_invalidity_date             R_CHALLENGE_IS_DIFFERENT                  X509_V_FLAG_USE_DELTAS
 NID_issuer_alt_name             R_CIPHER_TABLE_SRC_ERROR                  X509_V_FLAG_X509_STRICT
 NID_keyBag                      R_INVALID_CHALLENGE_LENGTH                X509_V_OK
 NID_key_usage                   R_NO_CERTIFICATE_SET                      XN_FLAG_COMPAT
 NID_localKeyID                  R_NO_CERTIFICATE_SPECIFIED                XN_FLAG_DN_REV
 NID_localityName                R_NO_CIPHER_LIST                          XN_FLAG_DUMP_UNKNOWN_FIELDS
 NID_md2                         R_NO_CIPHER_MATCH                         XN_FLAG_FN_ALIGN
 NID_md2WithRSAEncryption        R_NO_PRIVATEKEY                           XN_FLAG_FN_LN
 NID_md5                         R_NO_PUBLICKEY                            XN_FLAG_FN_MASK
 NID_md5WithRSA                  R_NULL_SSL_CTX                            XN_FLAG_FN_NONE
 NID_md5WithRSAEncryption        R_PEER_DID_NOT_RETURN_A_CERTIFICATE       XN_FLAG_FN_OID
 NID_md5_sha1                    R_PEER_ERROR                              XN_FLAG_FN_SN
 NID_mdc2                        R_PEER_ERROR_CERTIFICATE                  XN_FLAG_MULTILINE
 NID_mdc2WithRSA                 R_PEER_ERROR_NO_CIPHER                    XN_FLAG_ONELINE
 NID_ms_code_com                 R_PEER_ERROR_UNSUPPORTED_CERTIFICATE_TYPE XN_FLAG_RFC2253
 NID_ms_code_ind                 R_PUBLIC_KEY_ENCRYPT_ERROR                XN_FLAG_SEP_COMMA_PLUS
 NID_ms_ctl_sign                 R_PUBLIC_KEY_IS_NOT_RSA                   XN_FLAG_SEP_CPLUS_SPC
 NID_ms_efs                      R_READ_WRONG_PACKET_TYPE                  XN_FLAG_SEP_MASK
 NID_ms_ext_req                  R_SHORT_READ                              XN_FLAG_SEP_MULTILINE
 NID_ms_sgc                      R_SSL_SESSION_ID_IS_DIFFERENT             XN_FLAG_SEP_SPLUS_SPC
 NID_name                        R_UNABLE_TO_EXTRACT_PUBLIC_KEY            XN_FLAG_SPC_EQ

=head2 INTERNAL ONLY functions (do not use these)

The following functions are not intended for use from outside of L<Net::SSLeay> module.
They might be removed, renamed or changed without prior notice in future version.

Simply B<DO NOT USE THEM>!

=over

=item * hello

=item * blength

=item * constant

=back

=head1 EXAMPLES

One very good example to look at is the implementation of C<sslcat()> in the
C<SSLeay.pm> file.

The following is a simple SSLeay client (with too little error checking :-(

    #!/usr/bin/perl
    use Socket;
    use Net::SSLeay qw(die_now die_if_ssl_error) ;
    Net::SSLeay::load_error_strings();
    Net::SSLeay::SSLeay_add_ssl_algorithms();
    Net::SSLeay::randomize();

    ($dest_serv, $port, $msg) = @ARGV;      # Read command line
    $port = getservbyname ($port, 'tcp') unless $port =~ /^\d+$/;
    $dest_ip = gethostbyname ($dest_serv);
    $dest_serv_params  = sockaddr_in($port, $dest_ip);

    socket  (S, &AF_INET, &SOCK_STREAM, 0)  or die "socket: $!";
    connect (S, $dest_serv_params)          or die "connect: $!";
    select  (S); $| = 1; select (STDOUT);   # Eliminate STDIO buffering

    # The network connection is now open, lets fire up SSL

    $ctx = Net::SSLeay::CTX_new() or die_now("Failed to create SSL_CTX $!");
    Net::SSLeay::CTX_set_options($ctx, &Net::SSLeay::OP_ALL)
         or die_if_ssl_error("ssl ctx set options");
    $ssl = Net::SSLeay::new($ctx) or die_now("Failed to create SSL $!");
    Net::SSLeay::set_fd($ssl, fileno(S));   # Must use fileno
    $res = Net::SSLeay::connect($ssl) and die_if_ssl_error("ssl connect");
    print "Cipher `" . Net::SSLeay::get_cipher($ssl) . "'\n";

    # Exchange data

    $res = Net::SSLeay::write($ssl, $msg);  # Perl knows how long $msg is
    die_if_ssl_error("ssl write");
    CORE::shutdown S, 1;  # Half close --> No more output, sends EOF to server
    $got = Net::SSLeay::read($ssl);         # Perl returns undef on failure
    die_if_ssl_error("ssl read");
    print $got;

    Net::SSLeay::free ($ssl);               # Tear down connection
    Net::SSLeay::CTX_free ($ctx);
    close S;

The following is a simple SSLeay echo server (non forking):

    #!/usr/bin/perl -w
    use Socket;
    use Net::SSLeay qw(die_now die_if_ssl_error);
    Net::SSLeay::load_error_strings();
    Net::SSLeay::SSLeay_add_ssl_algorithms();
    Net::SSLeay::randomize();

    $our_ip = "\0\0\0\0"; # Bind to all interfaces
    $port = 1235;
    $sockaddr_template = 'S n a4 x8';
    $our_serv_params = pack ($sockaddr_template, &AF_INET, $port, $our_ip);

    socket (S, &AF_INET, &SOCK_STREAM, 0)  or die "socket: $!";
    bind (S, $our_serv_params)             or die "bind:   $!";
    listen (S, 5)                          or die "listen: $!";
    $ctx = Net::SSLeay::CTX_new ()         or die_now("CTX_new ($ctx): $!");
    Net::SSLeay::CTX_set_options($ctx, &Net::SSLeay::OP_ALL)
         or die_if_ssl_error("ssl ctx set options");

    # Following will ask password unless private key is not encrypted
    Net::SSLeay::CTX_use_RSAPrivateKey_file ($ctx, 'plain-rsa.pem',
                                             &Net::SSLeay::FILETYPE_PEM);
    die_if_ssl_error("private key");
    Net::SSLeay::CTX_use_certificate_file ($ctx, 'plain-cert.pem',
 				           &Net::SSLeay::FILETYPE_PEM);
    die_if_ssl_error("certificate");

    while (1) {
        print "Accepting connections...\n";
        ($addr = accept (NS, S))           or die "accept: $!";
        select (NS); $| = 1; select (STDOUT);  # Piping hot!

        ($af,$client_port,$client_ip) = unpack($sockaddr_template,$addr);
        @inetaddr = unpack('C4',$client_ip);
        print "$af connection from " .
        join ('.', @inetaddr) . ":$client_port\n";

        # We now have a network connection, lets fire up SSLeay...

        $ssl = Net::SSLeay::new($ctx)      or die_now("SSL_new ($ssl): $!");
        Net::SSLeay::set_fd($ssl, fileno(NS));

        $err = Net::SSLeay::accept($ssl) and die_if_ssl_error('ssl accept');
        print "Cipher `" . Net::SSLeay::get_cipher($ssl) . "'\n";

        # Connected. Exchange some data.

        $got = Net::SSLeay::read($ssl);     # Returns undef on fail
        die_if_ssl_error("ssl read");
        print "Got `$got' (" . length ($got) . " chars)\n";

        Net::SSLeay::write ($ssl, uc ($got)) or die "write: $!";
        die_if_ssl_error("ssl write");

        Net::SSLeay::free ($ssl);           # Tear down connection
        close NS;
    }

Yet another echo server. This one runs from C</etc/inetd.conf> so it avoids
all the socket code overhead. Only caveat is opening an rsa key file -
it had better be without any encryption or else it will not know where
to ask for the password. Note how C<STDIN> and C<STDOUT> are wired to SSL.

    #!/usr/bin/perl
    # /etc/inetd.conf
    #    ssltst stream tcp nowait root /path/to/server.pl server.pl
    # /etc/services
    #    ssltst		1234/tcp

    use Net::SSLeay qw(die_now die_if_ssl_error);
    Net::SSLeay::load_error_strings();
    Net::SSLeay::SSLeay_add_ssl_algorithms();
    Net::SSLeay::randomize();

    chdir '/key/dir' or die "chdir: $!";
    $| = 1;  # Piping hot!
    open LOG, ">>/dev/console" or die "Can't open log file $!";
    select LOG; print "server.pl started\n";

    $ctx = Net::SSLeay::CTX_new()     or die_now "CTX_new ($ctx) ($!)";
    $ssl = Net::SSLeay::new($ctx)     or die_now "new ($ssl) ($!)";
    Net::SSLeay::set_options($ssl, &Net::SSLeay::OP_ALL)
         and die_if_ssl_error("ssl set options");

    # We get already open network connection from inetd, now we just
    # need to attach SSLeay to STDIN and STDOUT
    Net::SSLeay::set_rfd($ssl, fileno(STDIN));
    Net::SSLeay::set_wfd($ssl, fileno(STDOUT));

    Net::SSLeay::use_RSAPrivateKey_file ($ssl, 'plain-rsa.pem',
                                         Net::SSLeay::FILETYPE_PEM);
    die_if_ssl_error("private key");
    Net::SSLeay::use_certificate_file ($ssl, 'plain-cert.pem',
                                       Net::SSLeay::FILETYPE_PEM);
    die_if_ssl_error("certificate");

    Net::SSLeay::accept($ssl) and die_if_ssl_err("ssl accept: $!");
    print "Cipher `" . Net::SSLeay::get_cipher($ssl) . "'\n";

    $got = Net::SSLeay::read($ssl);
    die_if_ssl_error("ssl read");
    print "Got `$got' (" . length ($got) . " chars)\n";

    Net::SSLeay::write ($ssl, uc($got)) or die "write: $!";
    die_if_ssl_error("ssl write");

    Net::SSLeay::free ($ssl);         # Tear down the connection
    Net::SSLeay::CTX_free ($ctx);
    close LOG;

There are also a number of example/test programs in the examples directory:

    sslecho.pl   -  A simple server, not unlike the one above
    minicli.pl   -  Implements a client using low level SSLeay routines
    sslcat.pl    -  Demonstrates using high level sslcat utility function
    get_page.pl  -  Is a utility for getting html pages from secure servers
    callback.pl  -  Demonstrates certificate verification and callback usage
    stdio_bulk.pl       - Does SSL over Unix pipes
    ssl-inetd-serv.pl   - SSL server that can be invoked from inetd.conf
    httpd-proxy-snif.pl - Utility that allows you to see how a browser
                          sends https request to given server and what reply
                          it gets back (very educative :-)
    makecert.pl  -  Creates a self signed cert (does not use this module)

=head1 INSTALLATION

See README and README.* in the distribution directory for installation guidance on a variety of platforms.

=head1 LIMITATIONS

C<Net::SSLeay::read()> uses an internal buffer of 32KB, thus no single read
will return more. In practice one read returns much less, usually
as much as fits in one network packet. To work around this,
you should use a loop like this:

    $reply = '';
    while ($got = Net::SSLeay::read($ssl)) {
        last if print_errs('SSL_read');
        $reply .= $got;
    }

Although there is no built-in limit in C<Net::SSLeay::write()>, the network
packet size limitation applies here as well, thus use:

    $written = 0;

    while ($written < length($message)) {
        $written += Net::SSLeay::write($ssl, substr($message, $written));
        last if print_errs('SSL_write');
    }

Or alternatively you can just use the following convenience functions:

    Net::SSLeay::ssl_write_all($ssl, $message) or die "ssl write failure";
    $got = Net::SSLeay::ssl_read_all($ssl) or die "ssl read failure";

=head1 KNOWN BUGS AND CAVEATS

An OpenSSL bug CVE-2015-0290 "OpenSSL Multiblock Corrupted Pointer Issue" 
can cause POST requests of over 90kB to fail or crash. This bug is reported to be fixed in
OpenSSL 1.0.2a.

Autoloader emits a

    Argument "xxx" isn't numeric in entersub at blib/lib/Net/SSLeay.pm'

warning if die_if_ssl_error is made autoloadable. If you figure out why,
drop me a line.

Callback set using C<SSL_set_verify()> does not appear to work. This may
well be an openssl problem (e.g. see C<ssl/ssl_lib.c> line 1029). Try using
C<SSL_CTX_set_verify()> instead and do not be surprised if even this stops
working in future versions.

Callback and certificate verification stuff is generally too little tested.

Random numbers are not initialized randomly enough, especially if you
do not have C</dev/random> and/or C</dev/urandom> (such as in Solaris
platforms - but it's been suggested that cryptorand daemon from the SUNski
package solves this). In this case you should investigate third party
software that can emulate these devices, e.g. by way of a named pipe
to some program.

Another gotcha with random number initialization is randomness
depletion. This phenomenon, which has been extensively discussed in
OpenSSL, Apache-SSL, and Apache-mod_ssl forums, can cause your
script to block if you use C</dev/random> or to operate insecurely
if you use C</dev/urandom>. What happens is that when too much
randomness is drawn from the operating system's randomness pool
then randomness can temporarily be unavailable. C</dev/random> solves
this problem by waiting until enough randomness can be gathered - and
this can take a long time since blocking reduces activity in the
machine and less activity provides less random events: a vicious circle.
C</dev/urandom> solves this dilemma more pragmatically by simply returning
predictable "random" numbers. SomeC< /dev/urandom> emulation software
however actually seems to implement C</dev/random> semantics. Caveat emptor.

I've been pointed to two such daemons by Mik Firestone <mik@@speed.stdio._com>
who has used them on Solaris 8:

=over

=item 1

Entropy Gathering Daemon (EGD) at L<http://www.lothar.com/tech/crypto/>

=item 2

Pseudo-random number generating daemon (PRNGD) at
L<http://www.aet.tu-cottbus.de/personen/jaenicke/postfix_tls/prngd.html>

=back

If you are using the low level API functions to communicate with other
SSL implementations, you would do well to call

    Net::SSLeay::CTX_set_options($ctx, &Net::SSLeay::OP_ALL)
         or die_if_ssl_error("ssl ctx set options");

to cope with some well know bugs in some other SSL
implementations. The high level API functions always set all known
compatibility options.

Sometimes C<sslcat()> (and the high level HTTPS functions that build on it)
is too fast in signaling the EOF to legacy HTTPS servers. This causes
the server to return empty page. To work around this problem you can
set the global variable

    $Net::SSLeay::slowly = 1;   # Add sleep so broken servers can keep up

HTTP/1.1 is not supported. Specifically this module does not know to
issue or serve multiple http requests per connection. This is a serious
shortcoming, but using the SSL session cache on your server helps to
alleviate the CPU load somewhat.

As of version 1.09 many newer OpenSSL auxiliary functions were
added (from C<REM_AUTOMATICALLY_GENERATED_1_09> onwards in C<SSLeay.xs>).
Unfortunately I have not had any opportunity to test these. Some of
them are trivial enough that I believe they "just work", but others
have rather complex interfaces with function pointers and all. In these
cases you should proceed wit great caution.

This module defaults to using OpenSSL automatic protocol negotiation
code for automatically detecting the version of the SSL/TLS protocol
that the other end talks. With most web servers this works just
fine, but once in a while I get complaints from people that the module
does not work with some web servers. Usually this can be solved
by explicitly setting the protocol version, e.g.

   $Net::SSLeay::ssl_version = 2;  # Insist on SSLv2
   $Net::SSLeay::ssl_version = 3;  # Insist on SSLv3
   $Net::SSLeay::ssl_version = 10; # Insist on TLSv1
   $Net::SSLeay::ssl_version = 11; # Insist on TLSv1.1
   $Net::SSLeay::ssl_version = 12; # Insist on TLSv1.2
   $Net::SSLeay::ssl_version = 13; # Insist on TLSv1.3

Although the autonegotiation is nice to have, the SSL standards
do not formally specify any such mechanism. Most of the world has
accepted the SSLeay/OpenSSL way of doing it as the de facto standard. But
for the few that think differently, you have to explicitly speak
the correct version. This is not really a bug, but rather a deficiency
in the standards. If a site refuses to respond or sends back some
nonsensical error codes (at the SSL handshake level), try this option
before mailing me.

On some systems, OpenSSL may be compiled without support for SSLv2.
If this is the case, Net::SSLeay will warn if ssl_version has been set
to 2.

The high level API returns the certificate of the peer, thus allowing
one to check what certificate was supplied. However, you will only be
able to check the certificate after the fact, i.e. you already sent
your form data by the time you find out that you did not trust them,
oops.

So, while being able to know the certificate after the fact is surely
useful, the security minded would still choose to do the connection
and certificate verification first and only then exchange data
with the site. Currently none of the high level API functions do
this, thus you would have to program it using the low level API. A
good place to start is to see how the C<Net::SSLeay::http_cat()> function
is implemented.

The high level API functions use a global file handle C<SSLCAT_S>
internally. This really should not be a problem because there is no
way to interleave the high level API functions, unless you use threads
(but threads are not very well supported in perl anyway). However, you
may run into problems if you call undocumented internal functions in an
interleaved fashion. The best solution is to "require Net::SSLeay" in
one thread after all the threads have been created.

=head1 DIAGNOSTICS

=over

=item Random number generator not seeded!!!

B<(W)> This warning indicates that C<randomize()> was not able to read
C</dev/random> or C</dev/urandom>, possibly because your system does not
have them or they are differently named. You can still use SSL, but
the encryption will not be as strong.

=item open_tcp_connection: destination host not found:`server' (port 123) ($!)

Name lookup for host named C<server> failed.

=item open_tcp_connection: failed `server', 123 ($!)

The name was resolved, but establishing the TCP connection failed.

=item msg 123: 1 - error:140770F8:SSL routines:SSL23_GET_SERVER_HELLO:unknown proto

SSLeay error string. The first number (123) is the PID, the second number
(1) indicates the position of the error message in SSLeay error stack.
You often see a pile of these messages as errors cascade.

=item msg 123: 1 - error:02001002::lib(2) :func(1) :reason(2)

The same as above, but you didn't call load_error_strings() so SSLeay
couldn't verbosely explain the error. You can still find out what it
means with this command:

    /usr/local/ssl/bin/ssleay errstr 02001002

=item Password is being asked for private key

This is normal behaviour if your private key is encrypted. Either
you have to supply the password or you have to use an unencrypted
private key. Scan OpenSSL.org for the FAQ that explains how to
do this (or just study examples/makecert.pl which is used
during C<make test> to do just that).

=back

=head1 SECURITY

You can mitigate some of the security vulnerabilities that might be present in your SSL/TLS application: 


=head2 BEAST Attack

http://blogs.cisco.com/security/beat-the-beast-with-tls/
https://community.qualys.com/blogs/securitylabs/2011/10/17/mitigating-the-beast-attack-on-tls
http://blog.zoller.lu/2011/09/beast-summary-tls-cbc-countermeasures.html

The BEAST attack relies on a weakness in the way CBC mode is used in SSL/TLS. 
In OpenSSL versions 0.9.6d and later, the protocol-level mitigation is enabled by default, 
thus making it not vulnerable to the BEAST attack.

Solutions:

=over

=item * Compile with OpenSSL versions 0.9.6d or later, which enables SSL_OP_ALL by default

=item * Ensure SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS is not enabled (its not enabled by default)

=item * Don't support SSLv2, SSLv3

=item * Actively control the ciphers your server supports with set_cipher_list:

=back

Net::SSLeay::set_cipher_list($ssl, 'RC4-SHA:HIGH:!ADH');


=head2 Session Resumption 

http://www.openssl.org/docs/ssl/SSL_CTX_set_options.html

The SSL Labs vulnerability test on your SSL server might report in red:

Session resumption      No (IDs assigned but not accepted)

This report is not really bug or a vulnerability, since the server will not 
accept session resumption requests.
However, you can prevent this noise in the report by disabling the session cache altogether:
Net::SSLeay::CTX_set_session_cache_mode($ssl_ctx, Net::SSLeay::SESS_CACHE_OFF());
Use 0 if you don't have SESS_CACHE_OFF constant.


=head2 Secure Renegotiation and DoS Attack

https://community.qualys.com/blogs/securitylabs/2011/10/31/tls-renegotiation-and-denial-of-service-attacks

This is not a "security flaw," it is more of a DoS vulnerability.

Solutions: 

=over

=item * Do not support SSLv2

=item * Do not set the SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION option

=item * Compile with OpenSSL 0.9.8m or later

=back

=head1 BUGS

If you encounter a problem with this module that you believe is a bug,
please report it in one of the following ways:

=over

=item *

L<create a new issue|https://github.com/radiator-software/p5-net-ssleay/issues/new>
under the Net-SSLeay GitHub project at
L<https://github.com/radiator-software/p5-net-ssleay>;

=item *

L<open a ticket|https://rt.cpan.org/Ticket/Create.html?Queue=Net-SSLeay> using
the CPAN RT bug tracker's web interface at
L<https://rt.cpan.org/Dist/Display.html?Queue=Net-SSLeay>;

=item *

send an email to the CPAN RT bug tracker at
L<bug-Net-SSLeay@rt.cpan.org|mailto:bug-Net-SSLeay@rt.cpan.org>.

=back

Please make sure your bug report includes the following information:

=over

=item * the code you are trying to run;

=item * your operating system name and version;

=item * the output of C<perl -V>;

=item * the version of OpenSSL or LibreSSL you are using.

=back

=head1 AUTHOR

Originally written by Sampo Kellomäki.

Maintained by Florian Ragwitz between November 2005 and January 2010.

Maintained by Mike McCauley between November 2005 and June 2018.

Maintained by Chris Novakovic, Tuure Vartiainen and Heikki Vatiainen since June 2018.

=head1 COPYRIGHT

Copyright (c) 1996-2003 Sampo Kellomäki <sampo@iki.fi>

Copyright (c) 2005-2010 Florian Ragwitz <rafl@debian.org>

Copyright (c) 2005-2018 Mike McCauley <mikem@airspayce.com>

Copyright (c) 2018- Chris Novakovic <chris@chrisn.me.uk>

Copyright (c) 2018- Tuure Vartiainen <vartiait@radiatorsoftware.com>

Copyright (c) 2018- Heikki Vatiainen <hvn@radiatorsoftware.com>

All rights reserved.

=head1 LICENSE

This module is released under the terms of the Artistic License 2.0. For
details, see the C<LICENSE> file distributed with Net-SSLeay's source code.

=head1 SEE ALSO

  Net::SSLeay::Handle                      - File handle interface
  ./examples                               - Example servers and a clients
  <http://www.openssl.org/>                - OpenSSL source, documentation, etc
  openssl-users-request@openssl.org        - General OpenSSL mailing list
  <http://www.ietf.org/rfc/rfc2246.txt>    - TLS 1.0 specification
  <http://www.w3c.org>                     - HTTP specifications
  <http://www.ietf.org/rfc/rfc2617.txt>    - How to send password
  <http://www.lothar.com/tech/crypto/>     - Entropy Gathering Daemon (EGD)
  <http://www.aet.tu-cottbus.de/personen/jaenicke/postfix_tls/prngd.html>
                           - pseudo-random number generating daemon (PRNGD)
  perl(1)
  perlref(1)
  perllol(1)
  perldoc ~openssl/doc/ssl/SSL_CTX_set_verify.pod
