Crypt::DSA(3)

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.