Crypt::...SSL::DSA(3)

📦
version 0.20 · 10 versions
, in alpine 3.24

💖 Crypt::...SSL::DSA(3) 💖

okay so bestie, welcome to the Crypt::...SSL::DSA(3) page from User Contributed Perl Documentation. The actual module is Crypt::OpenSSL::DSA, and we’re about to get into DSA with OpenSSL. buckle up. 🎀

🌸 NAME 🌸

Crypt::OpenSSL::DSA — Digital Signature Algorithm using OpenSSL.

✨ SYNOPSIS ✨

here’s the whole vibe in code, bestie — copy it exactly:

         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’s a thin XS wrapper to the DSA functions contained in the OpenSSL crypto library, located at http://www.openssl.org. No cap, it’s literally a thin wrapper. 💅

🎀 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. (The signature also lists $seed, but the original prose doesn’t describe it, so I’m not gonna invent tea about it. 🙈)

$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. (Yes, that spelling is straight from the page, bestie. 💀)

Comments, suggestions, and patches welcome. fr fr, send them in. 💌

🦋 AUTHOR 🦋

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

Copyright (c) 2002 T.J. Mather. Crypt::OpenSSL::DSA is free software; you may redistribute it and/or modify it under the same terms as Perl itself.

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

🔥 SEE ALSO 🔥

  • Crypt::OpenSSL::DSA::Signature
  • Crypt::DSA, Crypt::OpenSSL::RSA
  • Net::DNS::SEC

mwah 💋 — this page is from perl v5.42.2, dated 2025-06-30, and the footer tags it as Crypt::...SSL::DSA(3). byeee bestie 🫶

📦 where this page comes from