NAME

Crypt::OpenSSL::DSA - Digital Signature Algorithm using OpenSSL

SYNOPSIS

  use Crypt::OpenSSL::DSA;
  # generate keys and write out to PEM files
  my $dsa = Crypt::OpenSSL::DSA->generate_parameters( 512 );
  $dsa->generate_key;
  $dsa->write_pub_key( $filename );
  $dsa->write_priv_key( $filename );
  # using keys from PEM files
  my $dsa_priv = Crypt::OpenSSL::DSA->read_priv_key( $filename );
  my $sig      = $dsa_priv->sign($message);
  my $dsa_pub  = Crypt::OpenSSL::DSA->read_pub_key( $filename );
  my $valid    = $dsa_pub->verify($message, $sig);
  # using keys from PEM strings
  my $dsa_priv = Crypt::OpenSSL::DSA->read_priv_key_str( $key_string );
  my $sig      = $dsa_priv->sign($message);
  my $dsa_pub  = Crypt::OpenSSL::DSA->read_pub_key_str( $key_string );
  my $valid    = $dsa_pub->verify($message, $sig);

DESCRIPTION

Crypt::OpenSSL::DSA implements the DSA (Digital Signature Algorithm) signature verification system.

It is a thin XS wrapper to the DSA functions contained in the OpenSSL crypto library, located at http://www.openssl.org

CLASS METHODS

$dsa = Crypt::OpenSSL::DSA->generate_parameters( $bits, $seed );: Returns a new DSA object and generates the p, q and g parameters necessary to generate keys.
bits is the length of the prime to be generated; the DSS allows a maximum of 1024 bits.
$dsa = Crypt::OpenSSL::DSA->read_params( $filename );: Reads in a parameter PEM file and returns a new DSA object with the p, q and g parameters necessary to generate keys.
$dsa = Crypt::OpenSSL::DSA->read_pub_key( $filename );: Reads in a public key PEM file and returns a new DSA object that can be used to verify DSA signatures.
$dsa = Crypt::OpenSSL::DSA->read_priv_key( $filename );: Reads in a private key PEM file and returns a new DSA object that can be used to sign messages.
$dsa = Crypt::OpenSSL::DSA->read_pub_key_str( $key_string );: Reads in a public key PEM string and returns a new DSA object that can be used to verify DSA signatures. The string should include the -----BEGIN...----- and -----END...----- lines.
$dsa = Crypt::OpenSSL::DSA->read_priv_key_str( $key_string );: Reads in a private key PEM string and returns a new DSA object that can be used to sign messages. The string should include the -----BEGIN...----- and -----END...----- lines.

OBJECT METHODS

$dsa->generate_key;

Generates private and public keys, assuming that $dsa is the return value of generate_parameters.

$sig_size = $dsa->get_sig_size( );

Returns the maximum size of an ASN.1 encoded DSA signature for key dsa in bytes.

 512-bit keys = 48
1024-bit keys = 48
2024-bit keys = 72
3072-bit keys = 72

ASN.1 dsa signatures consist of:

Sequence 1-byte (0x30) Length 1-byte Integer 1-byte (0x02) Length 1-byte (0x14) = 20 r 20-bytes or 21-bytes Integer 1-byte (0x02) Length 1-byte (0x14) = 20 s 20-bytes or 21-bytes

30 2C 02 14 6C.70.50.7C.93.A8.B5.EC.1E.A1.5E.C5.73.AA.0F.EA.4D.BE.42.7A 02 14 4E.AD.E6.BB.72.54.92.30.2B.03.AB.53.5D.3D.6E.88.B8.AA.D6.30

Note that the above signature is 46 bytes long - the extra two bytes are used only when r and/or s are larger than or equal to 2^159. The extra bytes are used to distinguish positive from negative values.

All that to say if you are using get_sig_size() to determine the size of r + s depending on the size of the key you can subtract 8 bytes for the ASN.1 overhead.

$sig = $dsa->sign( $message );

Signs $message, returning the signature. Note that $meesage cannot exceed 20 characters in length.

$dsa is the signer's private key.

$sig_obj = $dsa->do_sign( $message );

Similar to "sign", but returns a Crypt::OpenSSL::DSA::Signature object.

$valid = $dsa->verify( $message, $sig );

Verifies that the $sig signature for $message is valid.

$dsa is the signer's public key.

Note: it croaks if the underlying library call returns error (-1).

$valid = $dsa->do_verify( $message, $sig_obj );

Similar to "verify", but uses a Crypt::OpenSSL::DSA::Signature object.

Note: it croaks if the underlying library call returns error (-1).

$dsa->write_params( $filename );

Writes the parameters into a PEM file.

$dsa->write_pub_key( $filename );

Writes the public key into a PEM file.

$dsa->write_priv_key( $filename );

Writes the private key into a PEM file.

$p = $dsa->get_p, $dsa->set_p($p)

Gets/sets the prime number in binary format.

$q = $dsa->get_q, $dsa->set_q($q)

Gets/sets the subprime number (q | p-1) in binary format.

$g = $dsa->get_g, $dsa->set_g($g)

Gets/sets the generator of subgroup in binary format.

$pub_key = $dsa->get_pub_key, $dsa->set_pub_key($pub_key)

Gets/sets the public key (y = g^x) in binary format.

$priv_key = $dsa->get_priv_key, $dsa->set_priv_key($priv_key)

Gets/sets the private key in binary format.

NOTES

Crpyt::DSA is a more mature Perl DSA module, but can be difficult to install, because of the Math::Pari requirement.

Comments, suggestions, and patches welcome.

AUTHOR

T.J. Mather, <tjmather@maxmind.com>

COPYRIGHT

Paid support is available directly from the author of this package. Please see <http://www.maxmind.com/app/opensourceservices> for more details.