Net::SSLeay - Perl extension for using OpenSSL

NAME

Net::SSLeay - Perl extension for using OpenSSL

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

DESCRIPTION

the Net::SSLeay manpage module contains perl bindings to openssl (http://www.openssl.org|http://www.openssl.org) library.

COMPATIBILITY NOTE: the Net::SSLeay manpage 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.

the Net::SSLeay manpage module basically comprise of:

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

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 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.

Basic set of functions

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 http://www.w3c.org.

Case 2 (in SYNOPSIS) demonstrates full fledged use of get_https(). As can be seen, 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 get_https() is used to insert some additional headers in the request. make_headers() is a function that will convert a list or hash to such headers. By default get_https() supplies Host (to make virtual hosting easy) and Accept (reportedly needed by IIS) headers.

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).

Case 3 (in SYNOPSIS) invokes post_https() to submit a HTML/CGI form to a secure server. The first four arguments are equal to get_https() (note that the empty string ('') 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 make_https() is used to do the formatting, but you could pass any string. post_https() automatically adds Content-Type and Content-Length headers to the request.

Case 4 (in SYNOPSIS) shows the fundamental sslcat() function (inspired in spirit by the 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 - sslcat() is just a transport.

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

The $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.

Alternate versions of high-level API

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 the perlref manpage and the perllol manpage 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 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 ds_https3() for guidance on how to do this.

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);

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.

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 VERIFY_PEER on the server:

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

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

Working through a web proxy

Net::SSLeay can use a web proxy to make its connections. You need to first set the proxy host and port using 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 "joe" and to the final web server as "susie". Proxy authentication requires the MIME::Base64 module to work.

HTTP (without S) API

Over the years it has become clear that it would be convenient to use the light-weight flavour API of Net::SSLeay for normal HTTP as well (see 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 "x" family of APIs takes as the first argument a flag which indicates whether SSL is used or not.

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 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 .r0, .r1 etc. For example ab1331b2.r0, 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).

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
        ...
    }

Using Net::SSLeay in multi-threaded applications

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 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:

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 int SSL_library_init(void) function (which is also aliased as SSLeay_add_ssl_algorithms, OpenSSL_add_ssl_algorithms and 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.

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.

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);

Using other perl modules based on Net::SSLeay

It should be fine to use any other module based on the Net::SSLeay manpage (like the IO::Socket::SSL manpage) in multi-threaded applications. It is generally recommended to do any global initialization of such a module in the main thread before calling threads->new(..) or 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();
    }

Combining Net::SSLeay with other modules linked with openssl

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 the Crypt::SSLeay manpage).

As it is expected that also ``another'' module will call 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).

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.

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);

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();

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.

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 fileno() to extract the underlying file descriptor:

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

You should also set $| 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 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). Net::SSLeay is no different from the C language OpenSSL in this respect.

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.

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 *.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 "SSL_" off of the SSLeay names. Generally you should use Net::SSLeay:: in its place.

Note that some functions are prefixed with "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 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

Low level API: Version related functions

Low level API: Initialization related functions

Low level API: ERR_* and SSL_alert_* related functions

NOTE: Please note that SSL_alert_* function have ``SSL_'' part stripped from their names.

Low level API: SSL_METHOD_* related functions

Low level API: ENGINE_* related functions

Low level API: EVP_PKEY_* related functions

Low level API: PEM_* related functions

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

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

Low level API: PKCS12 related functions

Low level API: SESSION_* related functions

Low level API: SSL_CTX_* related functions

NOTE: Please note that the function described in this chapter have ``SSL_'' part stripped from their original openssl names.

Low level API: SSL_* related functions

NOTE: Please note that the function described in this chapter have ``SSL_'' part stripped from their original openssl names.

Low level API: RAND_* related functions

Check openssl doc related to RAND stuff http://www.openssl.org/docs/crypto/rand.html|http://www.openssl.org/docs/crypto/rand.html

Low level API: OBJ_* related functions

Low level API: ASN1_INTEGER_* related functions

Low level API: ASN1_STRING_* related functions

Low level API: ASN1_TIME_* related functions

Low level API: X509_* related functions

Low level API: X509_REQ_* related functions

Low level API: X509_CRL_* related functions

Low level API: X509_EXTENSION_* related functions

Low level API: X509_NAME_* related functions

Low level API: X509_STORE_* related functions

Low Level API: X509_INFO related functions

Low level API: X509_VERIFY_PARAM_* related functions

Low level API: Cipher (EVP_CIPHER_*) related functions

Low level API: Digest (EVP_MD_*) related functions

Low level API: CIPHER_* related functions

Low level API: RSA_* related functions

Low level API: BIO_* related functions

Low level API: Server side Server Name Indication (SNI) support

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
 }

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
 }

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

Low level API: Other functions

Low level API: EC related functions

Constants

There are many openssl constants available in the Net::SSLeay manpage. 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 SSL_ prefix have name with SSL_ part stripped - e.g. openssl's constant SSL_OP_ALL is available as Net::SSleay::OP_ALL

The list of all available constant names:

 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

INTERNAL ONLY functions (do not use these)

The following functions are not intended for use from outside of the Net::SSLeay manpage module. They might be removed, renamed or changed without prior notice in future version.

Simply DO NOT USE THEM!

EXAMPLES

One very good example to look at is the implementation of sslcat() in the 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 /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 STDIN and 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)

INSTALLATION

See README and README.* in the distribution directory for installation guidance on a variety of platforms.

LIMITATIONS

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 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";

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 SSL_set_verify() does not appear to work. This may well be an openssl problem (e.g. see ssl/ssl_lib.c line 1029). Try using 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 /dev/random and/or /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 /dev/random or to operate insecurely if you use /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. /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. /dev/urandom solves this dilemma more pragmatically by simply returning predictable ``random'' numbers. Some /dev/urandom emulation software however actually seems to implement /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:

  1. Entropy Gathering Daemon (EGD) at http://www.lothar.com/tech/crypto/

  2. Pseudo-random number generating daemon (PRNGD) at http://www.aet.tu-cottbus.de/personen/jaenicke/postfix_tls/prngd.html

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 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 REM_AUTOMATICALLY_GENERATED_1_09 onwards in 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 Net::SSLeay::http_cat() function is implemented.

The high level API functions use a global file handle 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.

DIAGNOSTICS

Random number generator not seeded!!!
(W) This warning indicates that randomize() was not able to read /dev/random or /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.

open_tcp_connection: destination host not found:`server' (port 123) ($!)
Name lookup for host named server failed.

open_tcp_connection: failed `server', 123 ($!)
The name was resolved, but establishing the TCP connection failed.

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.

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

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 make test to do just that).

SECURITY

You can mitigate some of the security vulnerabilities that might be present in your SSL/TLS application:

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:

Net::SSLeay::set_cipher_list($ssl, 'RC4-SHA:HIGH:!ADH');

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.

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:

BUGS

If you encounter a problem with this module that you believe is a bug, please report it in one of the following ways:

Please make sure your bug report includes the following information:

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.

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.

LICENSE

This module is released under the terms of the Artistic License 2.0. For details, see the LICENSE file distributed with Net-SSLeay's source code.

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
 Net::SSLeay - Perl extension for using OpenSSL