Benjamin Trott
and 1 contributors


Crypt::DSA - DSA Signatures and Key Generation


    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,


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.


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


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::SHA1 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.


Benjamin Trott,

Except where otherwise noted, Crypt::DSA is Copyright 2001 Benjamin Trott. All rights reserved. Crypt::DSA is free software; you may redistribute it and/or modify it under the same terms as Perl itself.