IO::Socket::SSL

NAME
SYNOPSIS
DESCRIPTION
METHODS
DEBUGGING
EXAMPLES
BUGS
LIMITATIONS
DEPRECATIONS
SEE ALSO
AUTHORS
COPYRIGHT
Appendix: Using SSL

The Long of It (Detail)
The Short of It (Summary)

NAME

IO::Socket::SSL -- Nearly transparent SSL encapsulation for IO::Socket::INET.

SYNOPSIS

    use IO::Socket::SSL;

    my $client = new IO::Socket::SSL("www.example.com:https");

    if (defined $client) {
        print $client "GET / HTTP/1.0\r\n\r\n";
        print <$client>;
        close $client;
    } else {
        warn "I encountered a problem: ",
          &IO::Socket::SSL::errstr();
    }

DESCRIPTION

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 0.90 and above represent a complete rewrite of the IO::Socket::SSL internals.

METHODS

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 undefined value. The methods that have changed from the perspective of the user are re-documented here:

new(...): 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:
close(...): 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. $socket->close(SSL_no_shutdown => 1)) and one or more of the following parameters:
peek(): This function has exactly the same syntax as sysread(), and performs nearly the same task (reading data from the socket) but will not advance the read position so that successive calls to peek() with the same arguments will return the same results. This function requires Net::SSLeay v1.19 or higher and OpenSSL 0.9.6a or later to work.
pending(): This function will let you know how many bytes of data are immediately ready for reading from the socket. This is especially handy if you are doing reads on a blocking socket or just want to know if new data has been sent over the socket.
get_cipher(): Returns the string form of the cipher that the IO::Socket::SSL object is using.
dump_peer_certificate(): Returns a parsable string with select fields from the peer SSL certificate. This method directly returns the result of the dump_peer_certificate() method of Net::SSLeay.
peer_certificate($field): If a peer certificate exists, this function can retrieve values from it. Right now, the only fields it can return are ``authority'' and ``owner'' (or ``issuer'' and ``subject'' if you want to use OpenSSL names), corresponding to the certificate authority that signed the peer certificate and the owner of the peer certificate. This function returns a string with all the information about the particular field in one parsable line.
errstr(): 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.
IO::Socket::SSL::socket_to_SSL($socket, ... ): This will convert a glob reference or a socket that you provide to an IO::Socket::SSL object. You may also pass parameters to specify context or connection options as with a call to new(). If you are using this function on an accept()ed socket, you must set the parameter ``SSL_server'' to 1, i.e. IO::Socket::SSL::socket_to_SSL($socket, SSL_server => 1).

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:

truncate
stat
ungetc
setbuf
setvbuf
fdopen

DEBUGGING

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 4) to IO::Socket::SSL when calling it:

use IO::Socket::SSL qw(debug0);: #No debugging (default).
use IO::Socket::SSL qw(debug1);: #Only print out errors.
use IO::Socket::SSL qw(debug2);: #Print out errors and cipher negotiation.
use IO::Socket::SSL qw(debug3);: #Print out progress, ciphers, and errors.
use IO::Socket::SSL qw(debug4);: #Print out everything, including data.

You can also set $IO::Socket::SSL::DEBUG to 0-4, but that's a bit of a mouthful, isn't it?

EXAMPLES

See the 'example' directory.

BUGS

I have never shipped a module with a known bug, and IO::Socket::SSL is no different. If you feel that you have found a bug in the module and you are using the latest version of Net::SSLeay, send an email immediately to behroozi@www.pls.uni.edu with a subject of 'IO::Socket::SSL Bug'. I am not responsible for problems in your code, so make sure that an example actually works before sending it. It is merely acceptable if you send me a bug report, it is better if you send a small chunk of code that points it out, and it is best if you send a patch--if the patch is good, you might see a release the next day on CPAN. Otherwise, it could take weeks . . .

LIMITATIONS

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 (1.20 recommended) and OpenSSL (0.9.6g recommended) on your computer before using this module.

DEPRECATIONS

The following functions are deprecated and are only retained for compatibility:

context_init(): (use the SSL_reuse_ctx option if you want to re-use a context)
socketToSSL(): (renamed to socket_to_SSL())
get_peer_certificate() and friends: (use the peer_certificate() function instead)
want_read() and want_write(): (search for the appropriate string in errstr())

The following classes have been removed:

SSL_SSL: (not that you should have been directly accessing this anyway):
X509_Certificate: (but get_peer_certificate() will still Do The Right Thing)

AUTHORS

Peter Behroozi, behroozi@www.pls.uni.edu.

Marko Asplund, aspa@kronodoc.fi, was the original author of IO::Socket::SSL.

COPYRIGHT

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

Appendix: Using SSL

If you are unfamiliar with the way OpenSSL works, a good reference 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 Long of It (Detail)

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 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.

The Short of It (Summary)

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.