SSL(3)

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:

    SSL_version
        Sets the version of the SSL protocol used to transmit data. The default is SSLv2/3, which auto-negotiates between SSLv2 and SSLv3. You may specify 'SSLv2', 'SSLv3', or 'TLSv1' (case-insensitive) if you do not want this behavior.

    SSL_cipher_list
        If you do not care for the default list of ciphers ('ALL:!LOW:!EXP'), then look in the OpenSSL documentation (<http://www.openssl.org/docs/apps/ciphers.html#CIPHER_STRINGS>), and specify a different set with this option.

    SSL_use_cert
        If this is set, it forces IO::Socket::SSL to use a certificate and key, even if you are setting up an SSL client. If this is set to 0 (the default), then you will only need a certificate and key if you are setting up a server.

    SSL_key_file
        If your RSA private key is not in default place (certs/server-key.pem for servers, certs/client-key.pem for clients), then this is the option that you would use to specify a different location. Keys should be PEM formatted, and if they are encrypted, you will be prompted to enter a password before the socket is formed (unless you specified the SSL_passwd_cb option).

    SSL_cert_file
        If your SSL certificate is not in the default place (certs/server-cert.pem for servers, certs/client-cert.pem for clients), then you should use this option to specify the location of your certificate. Note that a key and certificate are only required for an SSL server, so you do not need to bother with these trifling options should you be setting up an unauthenticated client.

    SSL_passwd_cb
        If your private key is encrypted, you might not want the default password prompt from Net::SSLeay. This option takes a reference to a subroutine that should return the password required to decrypt your private key. Note that Net::SSLeay >= 1.16 is required for this to work.

    SSL_ca_file
        If you want to verify that the peer certificate has been signed by a reputable certificate authority, then you should use this option to locate the file containing the certificate(s) of the reputable certificate authorities if it is not already in the file certs/my-ca.pem.

    SSL_ca_path
        If you are unusually friendly with the OpenSSL documentation, you might have set yourself up a directory containing several trusted certificates as separate files as well as an index of the certificates. If you want to use that directory for validation purposes, and that directory is not ca/, then use this option to point IO::Socket::SSL to the right place to look.

    SSL_verify_mode
        This option sets the verification mode for the peer certificate. The default (0x00) does no authentication. You may combine 0x01 (verify peer), 0x02 (fail verification if no peer certificate exists; ignored for clients), and 0x04 (verify client once) to change the default.

    SSL_reuse_ctx
        If you have already set the above options (SSL_use_cert through SSL_verify_mode; 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. If you pass any context-related options, they will be ignored. Note that contrary to previous versions of IO::Socket::SSL, a global SSL context will not be implicitly used.

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:

    SSL_no_shutdown
        If set to a true value, this option will make close() not use the SSL_shutdown() call on the socket in question so that the close operation can complete without problems if you have used shutdown() or are working on a copy of a socket.

    SSL_ctx_free
        If you want to make sure that the SSL context of the socket is destroyed when you close it, set this option to a true value.

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)

SEE ALSO
IO::Socket::INET, Net::SSLeay.

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

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

COPYRIGHT
The rewrite of this module is Copyright (C) 2002 Peter Behroozi.

This module is 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.

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 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. 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>.