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.

SECURITY
    DSA (Digital Signature Algorithm) signatures are no longer considered
    to be adequate for security.   

    This module should only be used for verifying old signatures and
    should not be used for new signatures.

    That being said, some technologies still require DSA signatures even
    in 2024. Consider using other solutions or explicitly not using DSA
    signatures.

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>

    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.

