NAME

       Crypt::DSA - DSA Signatures and Key Generation

SYNOPSIS

           use Crypt::DSA;
           my $dsa = Crypt::DSA->new;

           my $key = $dsa->keygen(
                          Size      => 512,
                          Seed      => $seed,
                          Verbosity => 1
                     );

           my $sig = $dsa->sign(
                          Message   => "foo bar",
                          Key       => $key
                     );

           my $verified = $dsa->verify(
                          Message   => "foo bar",
                          Signature => $sig,
                          Key       => $key,
                     );

DESCRIPTION

       Crypt::DSA is an implementation of the DSA (Digital Signature Algorithm) signature
       verification system. The implementation itself is pure Perl, although the heavy-duty
       mathematics underneath are provided by the Math::Pari library.

       This package provides DSA signing, signature verification, and key generation.

USAGE

       The Crypt::DSA public interface is similar to that of Crypt::RSA. This was done
       intentionally.

   Crypt::DSA->new
       Constructs a new Crypt::DSA object. At the moment this isn't particularly useful in
       itself, other than being the object you need to do much else in the system.

       Returns the new object.

   $key = $dsa->keygen(%arg)
       Generates a new set of DSA keys, including both the public and private portions of the
       key.

       %arg can contain:

       •   Size

           The size in bits of the p value to generate. The q and g values are always 160 bits
           each.

           This argument is mandatory.

       •   Seed

           A seed with which q generation will begin. If this seed does not lead to a suitable
           prime, it will be discarded, and a new random seed chosen in its place, until a
           suitable prime can be found.

           This is entirely optional, and if not provided a random seed will be generated
           automatically.

       •   Verbosity

           Should be either 0 or 1. A value of 1 will give you a progress meter during p and q
           generation--this can be useful, since the process can be relatively long.

           The default is 0.

   $signature = $dsa->sign(%arg)
       Signs a message (or the digest of a message) using the private portion of the DSA key and
       returns the signature.

       The return value--the signature--is a Crypt::DSA::Signature object.

       %arg can include:

       •   Digest

           A digest to be signed. The digest should be 20 bytes in length or less.

           You must provide either this argument or Message (see below).

       •   Key

           The Crypt::DSA::Key object with which the signature will be generated. Should contain
           a private key attribute (priv_key).

           This argument is required.

       •   Message

           A plaintext message to be signed. If you provide this argument, sign will first
           produce a SHA1 digest of the plaintext, then use that as the digest to sign. Thus
           writing

               my $sign = $dsa->sign(Message => $message, ... );

           is a shorter way of writing

               use Digest::SHA qw( sha1 );
               my $sig = $dsa->sign(Digest => sha1( $message ), ... );

   $verified = $dsa->verify(%arg)
       Verifies a signature generated with sign. Returns a true value on success and false on
       failure.

       %arg can contain:

       •   Key

           Key of the signer of the message; a Crypt::DSA::Key object.  The public portion of the
           key is used to verify the signature.

           This argument is required.

       •   Signature

           The signature itself. Should be in the same format as returned from sign, a
           Crypt::DSA::Signature object.

           This argument is required.

       •   Digest

           The original signed digest whose length is less than or equal to 20 bytes.

           Either this argument or Message (see below) must be present.

       •   Message

           As above in sign, the plaintext message that was signed, a string of arbitrary length.
           A SHA1 digest of this message will be created and used in the verification process.

TODO

       Add ability to munge format of keys. For example, read/write keys from/to key files (SSH
       key files, etc.), and also write them in other formats.

SUPPORT

       Bugs should be reported via the CPAN bug tracker at

       http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Crypt-DSA
       <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Crypt-DSA>

       For other issues, contact the author.

AUTHOR

       Benjamin Trott <ben@sixapart.com>

COPYRIGHT

       Except where otherwise noted, Crypt::DSA is Copyright 2006 - 2011 Benjamin Trott.

       Crypt::DSA is free software; you may redistribute it and/or modify it under the same terms
       as Perl itself.