NAME

Crypt::PK::DSA - Public key cryptography based on DSA

SYNOPSIS

### OO interface

my $message = 'hello world';
my $signer = Crypt::PK::DSA->new();
$signer->generate_key(30, 256);

my $signature = $signer->sign_message($message);
my $public_der = $signer->export_key_der('public');
my $verifier = Crypt::PK::DSA->new(\$public_der);
$verifier->verify_message($signature, $message) or die "ERROR";

my $ciphertext = $verifier->encrypt("secret message");
my $plaintext = $signer->decrypt($ciphertext);

my $private_der = $signer->export_key_der('private');
my $private_pem = $signer->export_key_pem('private');
my $public_pem = $verifier->export_key_pem('public');

DESCRIPTION

DSA is primarily a digital signature scheme. In this module, signing and verification are the most common operations and therefore the primary examples.

Legacy function-style wrappers still exist in code for backwards compatibility, but they are intentionally undocumented.

METHODS

new

my $source = Crypt::PK::DSA->new();
$source->generate_key(20, 128);

my $public_der = $source->export_key_der('public');
my $pub = Crypt::PK::DSA->new(\$public_der);

my $private_pem = $source->export_key_pem('private', 'secret', 'AES-256-CBC');
my $priv = Crypt::PK::DSA->new(\$private_pem, 'secret');

Passing $filename or \$buffer to new is equivalent: both forms immediately import the key material into the new object.

generate_key

Uses the bundled chacha20 PRNG via libtomcrypt's rng_make_prng. Returns the object itself (for chaining).

$pk->generate_key($group_size, $modulus_size);
# $group_size  ... [integer] size of the subgroup (q) in bytes; must satisfy: 15 < $group_size < 1024
# $modulus_size .. [integer] size of the prime (p) in bytes; must satisfy: ($modulus_size - $group_size) < 512
#                  $modulus_size must be >= $group_size
#
# The two-integer form uses Perl's usual numeric-to-integer coercion before
# the XS call. Callers should therefore pass exact integers; values like
# C<10.9> or C<"1e1"> will be coerced according to Perl's integer conversion.

### Common parameter pairs (group_size, modulus_size) => security level:
# generate_key(20, 128)   => 80-bit security  (1024-bit p, 160-bit q)
# generate_key(30, 256)   => 120-bit security (2048-bit p, 240-bit q)
# generate_key(32, 256)   => 128-bit security (2048-bit p, 256-bit q)
# generate_key(35, 384)   => ~140-bit security (3072-bit p, 280-bit q)
# 140 bits  => generate_key(35, 384)
# 160 bits  => generate_key(40, 512)

### Sizes according section 4.2 of FIPS 186-4
# (L and N are the bit lengths of p and q respectively)
# L = 1024, N = 160 => generate_key(20, 128)
# L = 2048, N = 224 => generate_key(28, 256)
# L = 2048, N = 256 => generate_key(32, 256)
# L = 3072, N = 256 => generate_key(32, 384)

$pk->generate_key($param_hash)
# $param_hash is { p => $p, q => $q, g => $g }
# where $p, $q, $g are hex strings

$pk->generate_key(\$dsa_param)
# $dsa_param is the content of DER or PEM file with DSA params
# e.g. openssl dsaparam 2048

import_key

Loads private or public key in DER or PEM format.

my $source = Crypt::PK::DSA->new();
$source->generate_key(20, 128);

my $public_der = $source->export_key_der('public');
my $pub = Crypt::PK::DSA->new();
$pub->import_key(\$public_der);

my $private_pem = $source->export_key_pem('private', 'secret', 'AES-256-CBC');
my $priv = Crypt::PK::DSA->new();
$priv->import_key(\$private_pem, 'secret');

The same method also accepts filenames instead of buffers.

Loading private or public keys from a Perl HASH:

$pk->import_key($hashref);

# where $hashref is a key exported via key2hash
$pk->import_key({
  p => "AAF839A764E04D80824B79FA1F0496C093...", #prime modulus
  q => "D05C4CB45F29D353442F1FEC43A6BE2BE8...", #prime divisor
  g => "847E8896D12C9BF18FE283AE7AD58ED7F3...", #generator of a subgroup of order q in GF(p)
  x => "6C801901AC74E2DC714D75A9F6969483CF...", #private key, random  0 < x < q
  y => "8F7604D77FA62C7539562458A63C7611B7...", #public key, where y = g^x mod p
});

Supported key formats:

DSA public keys

DSA private keys

DSA private keys in password protected PEM format:

SSH public DSA keys

ssh-dss AAAAB3NzaC1kc3MAAACBAKU8/avmk...4XOwuEssAVhmwA==

SSH public DSA keys (RFC-4716 format)

---- BEGIN SSH2 PUBLIC KEY ----
Comment: "1024-bit DSA, converted from OpenSSH"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---- END SSH2 PUBLIC KEY ----

export_key_der

Returns the key as a binary DER-encoded string.

my $private_der = $pk->export_key_der('private');
#or
my $public_der = $pk->export_key_der('public');

export_key_pem

Returns the key as a PEM-encoded string (ASCII).

my $private_pem = $pk->export_key_pem('private');
#or
my $public_pem = $pk->export_key_pem('public');
#or
my $public_pem = $pk->export_key_pem('public_x509');

With parameter 'public' uses header and footer lines:

-----BEGIN DSA PUBLIC KEY------
-----END DSA PUBLIC KEY------

With parameter 'public_x509' uses header and footer lines:

-----BEGIN PUBLIC KEY------
-----END PUBLIC KEY------

Support for password protected PEM keys

my $private_pem = $pk->export_key_pem('private', $password);
#or
my $private_pem = $pk->export_key_pem('private', $password, $cipher);

# supported ciphers: 'DES-CBC'
#                    'DES-EDE3-CBC'
#                    'SEED-CBC'
#                    'CAMELLIA-128-CBC'
#                    'CAMELLIA-192-CBC'
#                    'CAMELLIA-256-CBC'
#                    'AES-128-CBC'
#                    'AES-192-CBC'
#                    'AES-256-CBC' (DEFAULT)

encrypt

Returns the ciphertext as a binary string.

DSA is usually used for signatures. This helper is available because the underlying library exposes a DSA-based encryption primitive.

my $pk = Crypt::PK::DSA->new($pub_key_filename);
my $ct = $pk->encrypt($message);
#or
my $ct = $pk->encrypt($message, $hash_name);

# $hash_name .. [string] 'SHA1' (DEFAULT), 'SHA256' or any other hash supported by Crypt::Digest

decrypt

Returns the plaintext as a binary string.

my $pk = Crypt::PK::DSA->new($priv_key_filename);
my $pt = $pk->decrypt($ciphertext);

sign_message

Returns the signature as a binary string.

my $pk = Crypt::PK::DSA->new($priv_key_filename);
my $signature = $pk->sign_message($message);
#or
my $signature = $pk->sign_message($message, $hash_name);

# $hash_name .. [string] 'SHA1' (DEFAULT), 'SHA256' or any other hash supported by Crypt::Digest

verify_message

Returns 1 if the signature is valid, 0 otherwise.

my $pk = Crypt::PK::DSA->new($pub_key_filename);
my $valid = $pk->verify_message($signature, $message);
#or
my $valid = $pk->verify_message($signature, $message, $hash_name);

# $hash_name .. [string] 'SHA1' (DEFAULT), 'SHA256' or any other hash supported by Crypt::Digest

sign_hash

Returns the signature as a binary string.

my $pk = Crypt::PK::DSA->new($priv_key_filename);
my $signature = $pk->sign_hash($message_hash);

verify_hash

Returns 1 if the signature is valid, 0 otherwise.

my $pk = Crypt::PK::DSA->new($pub_key_filename);
my $valid = $pk->verify_hash($signature, $message_hash);

is_private

my $rv = $pk->is_private;
# 1 .. private key loaded
# 0 .. public key loaded
# undef .. no key loaded

size

my $size = $pk->size;
# returns key size (length of the prime p) in bytes or undef if key not loaded

size_q

my $size = $pk->size_q;
# returns length of the prime q in bytes or undef if key not loaded

key2hash

Returns a hashref with the key components, or undef if no key is loaded.

my $hash = $pk->key2hash;

# returns hash like this (or undef if no key loaded):
{
  type => 1,   # integer: 1 .. private, 0 .. public
  size => 256, # integer: key size in bytes
  # all the rest are hex strings
  p => "AAF839A764E04D80824B79FA1F0496C093...", #prime modulus
  q => "D05C4CB45F29D353442F1FEC43A6BE2BE8...", #prime divisor
  g => "847E8896D12C9BF18FE283AE7AD58ED7F3...", #generator of a subgroup of order q in GF(p)
  x => "6C801901AC74E2DC714D75A9F6969483CF...", #private key, random  0 < x < q
  y => "8F7604D77FA62C7539562458A63C7611B7...", #public key, where y = g^x mod p
}

OpenSSL interoperability

### let's have:
# DSA private key in PEM format - dsakey.priv.pem
# DSA public key in PEM format  - dsakey.pub.pem
# data file to be signed - input.data

Sign by OpenSSL, verify by Crypt::PK::DSA

Create signature (from commandline):

openssl dgst -sha1 -sign dsakey.priv.pem -out input.sha1-dsa.sig input.data

Verify signature (Perl code):

use Crypt::PK::DSA;
use Crypt::Digest 'digest_file';
use Crypt::Misc 'read_rawfile';

my $pkdsa = Crypt::PK::DSA->new("dsakey.pub.pem");
my $signature = read_rawfile("input.sha1-dsa.sig");
my $valid = $pkdsa->verify_hash($signature, digest_file("SHA1", "input.data"));
print $valid ? "SUCCESS" : "FAILURE";

Sign by Crypt::PK::DSA, verify by OpenSSL

Create signature (Perl code):

use Crypt::PK::DSA;
use Crypt::Digest 'digest_file';
use Crypt::Misc 'write_rawfile';

my $pkdsa = Crypt::PK::DSA->new("dsakey.priv.pem");
my $signature = $pkdsa->sign_hash(digest_file("SHA1", "input.data"));
write_rawfile("input.sha1-dsa.sig", $signature);

Verify signature (from commandline):

openssl dgst -sha1 -verify dsakey.pub.pem -signature input.sha1-dsa.sig input.data

Keys generated by Crypt::PK::DSA

Generate keys (Perl code):

use Crypt::PK::DSA;
use Crypt::Misc 'write_rawfile';

my $pkdsa = Crypt::PK::DSA->new;
$pkdsa->generate_key(20, 128);
write_rawfile("dsakey.pub.der",  $pkdsa->export_key_der('public'));
write_rawfile("dsakey.priv.der", $pkdsa->export_key_der('private'));
write_rawfile("dsakey.pub.pem",  $pkdsa->export_key_pem('public_x509'));
write_rawfile("dsakey.priv.pem", $pkdsa->export_key_pem('private'));
write_rawfile("dsakey-passwd.priv.pem", $pkdsa->export_key_pem('private', 'secret'));

Use keys by OpenSSL:

openssl dsa -in dsakey.priv.der -text -inform der
openssl dsa -in dsakey.priv.pem -text
openssl dsa -in dsakey-passwd.priv.pem -text -inform pem -passin pass:secret
openssl dsa -in dsakey.pub.der -pubin -text -inform der
openssl dsa -in dsakey.pub.pem -pubin -text

Keys generated by OpenSSL

Generate keys:

openssl dsaparam -genkey -out dsakey.priv.pem 1024
openssl dsa -in dsakey.priv.pem -out dsakey.priv.der -outform der
openssl dsa -in dsakey.priv.pem -out dsakey.pub.pem -pubout
openssl dsa -in dsakey.priv.pem -out dsakey.pub.der -outform der -pubout
openssl dsa -in dsakey.priv.pem -passout pass:secret -des3 -out dsakey-passwd.priv.pem

Load keys (Perl code):

use Crypt::PK::DSA;

my $pkdsa = Crypt::PK::DSA->new;
$pkdsa->import_key("dsakey.pub.der");
$pkdsa->import_key("dsakey.priv.der");
$pkdsa->import_key("dsakey.pub.pem");
$pkdsa->import_key("dsakey.priv.pem");
$pkdsa->import_key("dsakey-passwd.priv.pem", "secret");

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