# phpman > perldoc > Crypt::DSA

## NAME
    [Crypt::DSA](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADSA/markdown) - DSA Signatures and Key Generation

## SYNOPSIS
        use [Crypt::DSA](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADSA/markdown);
        my $dsa = [Crypt::DSA](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADSA/markdown)->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](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADSA/markdown)* 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](https://www.chedong.com/phpMan.php/perldoc/Math%3A%3APari/markdown)* library.

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

## USAGE
    The *[Crypt::DSA](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADSA/markdown)* public interface is similar to that of *[Crypt::RSA](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ARSA/markdown)*. This was done
    intentionally.

  [Crypt::DSA](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADSA/markdown)->new
    Constructs a new *[Crypt::DSA](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADSA/markdown)* 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](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADSA%3A%3ASignature/markdown)* 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](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADSA%3A%3AKey/markdown)* 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](https://www.chedong.com/phpMan.php/perldoc/Digest%3A%3ASHA/markdown) 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](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADSA%3A%3AKey/markdown)* 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](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADSA%3A%3ASignature/markdown)* 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](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADSA/markdown) is Copyright 2006 - 2011 Benjamin Trott.

    [Crypt::DSA](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3ADSA/markdown) is free software; you may redistribute it and/or modify it under the same terms as
    Perl itself.