IO::Socket::SSL -- Nearly transparent SSL encapsulation for IO::Socket::INET.
use strict;
use IO::Socket::SSL;
my $client = IO::Socket::SSL->new("www.example.com:https")
|| warn "I encountered a problem: ".IO::Socket::SSL::errstr();
$client->verify_hostname( 'www.example.com','http' )
|| die "hostname verification failed";
print $client "GET / HTTP/1.0\r\n\r\n";
print <$client>;
This module is a true drop-in replacement for IO::Socket::INET that uses SSL to encrypt data before it is transferred to a remote server or client. IO::Socket::SSL supports all the extra features that one needs to write a full-featured SSL client or server application: multiple SSL contexts, cipher selection, certificate verification, and SSL version selection. As an extra bonus, it works perfectly with mod_perl.
If you have never used SSL before, you should read the appendix labelled 'Using SSL' before attempting to use this module.
If you have used this module before, read on, as versions 0.93 and above have several changes from the previous IO::Socket::SSL versions (especially see the note about return values).
If you are using non-blocking sockets read on, as version 0.98 added better support for non-blocking.
If you are trying to use it with threads see the BUGS section.
IO::Socket::SSL inherits its methods from IO::Socket::INET, overriding them as necessary. If there is an SSL error, the method or operation will return an empty list (false in all contexts). The methods that have changed from the perspective of the user are re-documented here:
Creates a new IO::Socket::SSL object. You may use all the friendly options that came bundled with IO::Socket::INET, plus (optionally) the ones that follow:
Set the name which is used in verification of hostname. If SSL_verifycn_scheme is set and no SSL_verifycn_name is given it will try to use the PeerHost and PeerAddr settings and fail if no name caan be determined.
Using PeerHost or PeerAddr works only if you create the connection directly
with IO::Socket::SSL->new, if an IO::Socket::INET object is upgraded
with start_SSL the name has to be given in SSL_verifycn_name.
If you have already set the above options (SSL_version through SSL_check_crl; this does not include SSL_cipher_list yet) for a previous instance of IO::Socket::SSL, then you can reuse the SSL context of that instance by passing it as the value for the SSL_reuse_ctx parameter. You may also create a new instance of the IO::Socket::SSL::SSL_Context class, using any context options that you desire without specifying connection options, and pass that here instead.
If you use this option, all other context-related options that you pass in the same call to new() will be ignored unless the context supplied was invalid. Note that, contrary to versions of IO::Socket::SSL below v0.90, a global SSL context will not be implicitly used unless you use the set_default_context() function.
Specifies session cache object which should be used instead of creating a new. Overrules SSL_session_cache_size. This option is useful if you wan't to reuse the cache, but not the rest of the context.
A session cache object can be created using
IO::Socket::SSL::Session_Cache->new( cachesize ).
Use set_default_session_cache() to set a global cache object.
There are a number of nasty traps that lie in wait if you are not careful about using close(). The first of these will bite you if you have been using shutdown() on your sockets. Since the SSL protocol mandates that a SSL "close notify" message be sent before the socket is closed, a shutdown() that closes the socket's write channel will cause the close() call to hang. For a similar reason, if you try to close a copy of a socket (as in a forking server) you will affect the original socket as well. To get around these problems, call close with an object-oriented syntax (e.g. $socket->close(SSL_no_shutdown => 1)) and one or more of the following parameters:
If a peer certificate exists, this function can retrieve values from it. If no field is given the internal representation of certificate from Net::SSLeay is returned. The following fields can be queried:
Alternative names for the subject, usually different names for the same server, like example.org, example.com, *.example.com.
It returns a list of (typ,value) with typ GEN_DNS, GEN_IPADD etc (these constants are exported from IO::Socket::SSL). See Net::SSLeay::X509_get_subjectAltNames.
This verifies the given hostname against the peer certificate using the given scheme. Hostname is usually what you specify within the PeerAddr.
Verification of hostname against a certificate is different between various applications and RFCs. Some scheme allow wildcards for hostnames, some only in subjectAltNames, and even their different wildcard schemes are possible.
To ease the verification the following schemes are predefined:
The scheme can be given either by specifying the name for one of the above predefined schemes, by using a callback (see below) or by using a hash which can have the following keys and values:
If you give a subroutine for verification it will be called with the arguments ($hostname,$commonName,@subjectAltNames), where hostname is the name given for verification, commonName is the result from peer_certificate('cn') and subjectAltNames is the result from peer_certificate('subjectAltNames').
Returns the last error (in string form) that occurred. If you do not have a real object to perform this method on, call IO::Socket::SSL::errstr() instead.
For read and write errors on non-blocking sockets, this method may include the string
SSL wants a read first! or SSL wants a write first! meaning that the other side
is expecting to read from or write to the socket and wants to be satisfied before you
get to do anything. But with version 0.98 you are better comparing the global exported
variable $SSL_ERROR against the exported symbols SSL_WANT_READ and SSL_WANT_WRITE.
This will convert a glob reference or a socket that you provide to an IO::Socket::SSL object. You may also pass parameters to specify context or connection options as with a call to new(). If you are using this function on an accept()ed socket, you must set the parameter "SSL_server" to 1, i.e. IO::Socket::SSL->start_SSL($socket, SSL_server => 1). If you have a class that inherits from IO::Socket::SSL and you want the $socket to be blessed into your own class instead, use MyClass->start_SSL($socket) to achieve the desired effect.
Note that if start_SSL() fails in SSL negotiation, $socket will remain blessed in its original class. For non-blocking sockets you better just upgrade the socket to IO::Socket::SSL and call accept_SSL or connect_SSL and the upgraded object. To just upgrade the socket set SSL_startHandshake explicitly to 0. If you call start_SSL w/o this parameter it will revert to blocking behavior for accept_SSL and connect_SSL.
If given the parameter "Timeout" it will stop if after the timeout no SSL connection was established. This parameter is only used for blocking sockets, if it is not given the default Timeout from the underlying IO::Socket will be used.
This is the opposite of start_SSL(), e.g. it will shutdown the SSL connection and return to the class before start_SSL(). It gets the same arguments as close(), in fact close() calls stop_SSL() (but without downgrading the class).
Will return true if it suceeded and undef if failed. This might be the case for non-blocking sockets. In this case $! is set to EAGAIN and the ssl error to SSL_WANT_READ or SSL_WANT_WRITE. In this case the call should be retried again with the same arguments once the socket is ready is until it succeeds.
With this function one can set defaults for all SSL_* parameter used for creation of the context, like the SSL_verify* parameter.
The following methods are unsupported (not to mention futile!) and IO::Socket::SSL will emit a large CROAK() if you are silly enough to use them:
A few changes have gone into IO::Socket::SSL v0.93 and later with respect to
return values. The behavior on success remains unchanged, but for all functions,
the return value on error is now an empty list. Therefore, the return value will be
false in all contexts, but those who have been using the return values as arguments
to subroutines (like mysub(IO::Socket::SSL(...)-new, ...)>) may run into problems.
The moral of the story: always check the return values of these functions before
using them in any way that you consider meaningful.
Support for IPv6 with IO::Socket::SSL is expected to work, but is experimental, as
none of the author's machines use IPv6 and hence he cannot test IO::Socket::SSL with
them. However, a few brave people have used it without incident, so if you wish to
make IO::Socket::SSL IPv6 aware, pass the 'inet6' option to IO::Socket::SSL when
calling it (i.e. use IO::Socket::SSL qw(inet6);). You will need IO::Socket::INET6
and Socket6 to use this option, and you will also need to write use Socket6; before
using IO::Socket::SSL. If you absolutely do not want to use this (or want a quick
change back to IPv4), pass the 'inet4' option instead.
Currently, there is no support for using IPv4 and IPv6 simultaneously in a single program, but it is planned for a future release.
If you are having problems using IO::Socket::SSL despite the fact that can recite backwards the section of this documentation labelled 'Using SSL', you should try enabling debugging. To specify the debug level, pass 'debug#' (where # is a number from 0 to 3) to IO::Socket::SSL when calling it. The debug level will also be propagated to Net::SSLeay::trace, see also Net::SSLeay:
See the 'example' directory.
IO::Socket::SSL is not threadsafe. This is because IO::Socket::SSL is based on Net::SSLeay which uses a global object to access some of the API of openssl and is therefore not threadsafe. It might probably work if you don't use SSL_verify_callback and SSL_password_cb.
IO::Socket::SSL does not work together with Storable::fd_retrieve/fd_store. See BUGS file for more information and how to work around the problem.
IO::Socket::SSL uses Net::SSLeay as the shiny interface to OpenSSL, which is the shiny interface to the ugliness of SSL. As a result, you will need both Net::SSLeay and OpenSSL on your computer before using this module.
If you have Scalar::Util (standard with Perl 5.8.0 and above) or WeakRef, IO::Socket::SSL sockets will auto-close when they go out of scope, just like IO::Socket::INET sockets. If you do not have one of these modules, then IO::Socket::SSL sockets will stay open until the program ends or you explicitly close them. This is due to the fact that a circular reference is required to make IO::Socket::SSL sockets act simultaneously like objects and glob references.
The following functions are deprecated and are only retained for compatibility:
The following classes have been removed:
IO::Socket::INET, IO::Socket::INET6, Net::SSLeay.
Steffen Ullrich, <steffen at genua.de> is the current maintainer.
Peter Behroozi, <behrooz at fas.harvard.edu> (Note the lack of an "i" at the end of "behrooz")
Marko Asplund, <marko.asplund at kronodoc.fi>, was the original author of IO::Socket::SSL.
Patches incorporated from various people, see file Changes.
Working support for non-blocking was added by Steffen Ullrich.
The rewrite of this module is Copyright (C) 2002-2005 Peter Behroozi.
The original versions of this module are Copyright (C) 1999-2002 Marko Asplund.
This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
If you are unfamiliar with the way OpenSSL works, good references may be found in both the book "Network Security with OpenSSL" (Oreilly & Assoc.) and the web site http://www.tldp.org/HOWTO/SSL-Certificates-HOWTO/. Read on for a quick overview.
The usual reason for using SSL is to keep your data safe. This means that not only do you have to encrypt the data while it is being transported over a network, but you also have to make sure that the right person gets the data. To accomplish this with SSL, you have to use certificates. A certificate closely resembles a Government-issued ID (at least in places where you can trust them). The ID contains some sort of identifying information such as a name and address, and is usually stamped with a seal of Government Approval. Theoretically, this means that you may trust the information on the card and do business with the owner of the card. The same ideas apply to SSL certificates, which have some identifying information and are "stamped" [most people refer to this as signing instead] by someone (a Certificate Authority) who you trust will adequately verify the identifying information. In this case, because of some clever number theory, it is extremely difficult to falsify the stamping process. Another useful consequence of number theory is that the certificate is linked to the encryption process, so you may encrypt data (using information on the certificate) that only the certificate owner can decrypt.
What does this mean for you? It means that at least one person in the party has to have an ID to get drinks :-). Seriously, it means that one of the people communicating has to have a certificate to ensure that your data is safe. For client/server interactions, the server must always have a certificate. If the server wants to verify that the client is safe, then the client must also have a personal certificate. To verify that a certificate is safe, one compares the stamped "seal" [commonly called an encrypted digest/hash/signature] on the certificate with the official "seal" of the Certificate Authority to make sure that they are the same. To do this, you will need the [unfortunately named] certificate of the Certificate Authority. With all these in hand, you can set up a SSL connection and be reasonably confident that no-one is reading your data.
For servers, you will need to generate a cryptographic private key and a certificate request. You will need to send the certificate request to a Certificate Authority to get a real certificate back, after which you can start serving people. For clients, you will not need anything unless the server wants validation, in which case you will also need a private key and a real certificate. For more information about how to get these, see http://www.modssl.org/docs/2.8/ssl_faq.html#ToC24.