Reference

Crypt::PK::DSA(3pm)

Public key cryptography based on DSA

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, 'SHA256');
 my $public_der = $signer->export_key_der('public');
 my $verifier = Crypt::PK::DSA->new(\$public_der);
 $verifier->verify_message($signature, $message, 'SHA256') 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

 -----BEGIN PUBLIC KEY-----
 MIIBtjCCASsGByqGSM44BAEwggEeAoGBAJKyu+puNMGLpGIhbD1IatnwlI79ePr4
 YHe2KBhRkheKxWUZRpN1Vd/+usS2IHSJ9op5cSWETiP05d7PMtJaitklw7jhudq3
 GxNvV/GRdCQm3H6d76FHP88dms4vcDYc6ry6wKERGfNEtZ+4BAKrMZK+gDYsF4Aw
 U6WVR969kYZhAhUA6w25FgSRmJ8W4XkvC60n8Wv3DpMCgYA4ZFE+3tLOM24PZj9Z
 rxuqUzZZdR+kIzrsIYpWN9ustbmdKLKwsqIaUIxc5zxHEhbAjAIf8toPD+VEQIpY
 7vgJgDhXuPq45BgN19iLTzOJwIhAFXPZvnAdIo9D/AnMw688gT6g6U8QCZwX2XYg
 ICiVcriYVNcjVKHSFY/X0Oi7CgOBhAACgYB4ZTn4OYT/pjUd6tNhGPtOS3CE1oaj
 5ScbetXg4ZDpceEyQi8VG+/ZTbs8var8X77JdEdeQA686cAxpOaVgW8V4odvcmfA
 BfueiGnPXjqGfppiHAyL1Ngyd+EsXKmKVXZYAVFVI0WuJKiZBSVURU7+ByxOfpGa
 fZhibr0SggWixQ==
 -----END PUBLIC KEY-----
•

DSA private keys

 -----BEGIN DSA PRIVATE KEY-----
 MIIBuwIBAAKBgQCSsrvqbjTBi6RiIWw9SGrZ8JSO/Xj6+GB3tigYUZIXisVlGUaT
 dVXf/rrEtiB0ifaKeXElhE4j9OXezzLSWorZJcO44bnatxsTb1fxkXQkJtx+ne+h
 Rz/PHZrOL3A2HOq8usChERnzRLWfuAQCqzGSvoA2LBeAMFOllUfevZGGYQIVAOsN
 uRYEkZifFuF5LwutJ/Fr9w6TAoGAOGRRPt7SzjNuD2Y/Wa8bqlM2WXUfpCM67CGK
 VjfbrLW5nSiysLKiGlCMXOc8RxIWwIwCH/LaDw/lRECKWO74CYA4V7j6uOQYDdfY
 i08zicCIQBVz2b5wHSKPQ/wJzMOvPIE+oOlPEAmcF9l2ICAolXK4mFTXI1Sh0hWP
 19DouwoCgYB4ZTn4OYT/pjUd6tNhGPtOS3CE1oaj5ScbetXg4ZDpceEyQi8VG+/Z
 Tbs8var8X77JdEdeQA686cAxpOaVgW8V4odvcmfABfueiGnPXjqGfppiHAyL1Ngy
 d+EsXKmKVXZYAVFVI0WuJKiZBSVURU7+ByxOfpGafZhibr0SggWixQIVAL7Sia03
 8bvANjjL9Sitk8slrM6P
 -----END DSA PRIVATE KEY-----
•

DSA private keys in password protected PEM format:

 -----BEGIN DSA PRIVATE KEY-----
 Proc-Type: 4,ENCRYPTED
 DEK-Info: DES-CBC,227ADC3AA0299491
 UISxBYAxPQMl2eK9LMAeHsssF6IxO+4G2ta2Jn8VE+boJrrH3iSTKeMXGjGaXl0z
 DwcLGV+KMR70y+cxtTb34rFy+uSpBy10dOQJhxALDbe1XfCDQIUfaXRfMNA3um2I
 JdZixUD/zcxBOUzao+MCr0V9XlJDgqBhJ5EEr53XHH07Eo5fhiBfbbR9NzdUPFrQ
 p2ASyZtFh7RXoIBUCQgg21oeLddcNWV7gd/Y46kghO9s0JbJ8C+IsuWEPRSq502h
 tSoDN6B0sxbVvOUICLLbQaxt7yduTAhRxVIJZ1PWATTVD7CZBVz9uIDZ7LOv+er2
 1q3vkwb8E9spPsA240+BnfD571XEop4jrawxC0VKQZ+3cPVLc6jhIsxvzzFQUt67
 g66v8GUgt7KF3KhVV7qEtntybQWDWb+K/uTIH9Ra8nP820d3Rnl61pPXDPlluteT
 WSLOvEMN2zRmkaxQNv/tLdT0SYpQtdjw74G3A6T7+KnvinKrjtp1a/AXkCF9hNEx
 DGbxOYo1UOmk8qdxWCrab34nO+Q8oQc9wjXHG+ZtRYIMoGMKREK8DeL4H1RPNkMf
 rwXWk8scd8QFmJAb8De1VQ==
 -----END DSA PRIVATE KEY-----
•

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"
 AAAAB3NzaC1kc3MAAACBAKU8/avmkFeGnSqwYG7dZnQlG+01QNaxu3F5v0NcL/SRUW7Idp
 Uq8t14siK0mA6yjphLhOf5t8gugTEVBllP86ANSbFigH7WN3v6ydJWqm60pNhNHN//50cn
 NtIsXbxeq3VtsI64pkH1OJqeZDHLmu73k4T0EKOzsylSfF/wtVBJAAAAFQChpubLHViwPB
 +jSvUb8e4THS7PBQAAAIAJD1PMCiTCQa1xyD/NCWOajCufTOIzKAhm6l+nlBVPiKI+262X
 pYt127Ke4mPL8XJBizoTjSQN08uHMg/8L6W/cdO2aZ+mhkBnS1xAm83DAwqLrDraR1w/4Q
 RFxr5Vbyy8qnejrPjTJobBN1BGsv84wHkjmoCn6pFIfkGYeATlJgAAAIAHYPU1zMVBTDWr
 u7SNC4G2UyWGWYYLjLytBVHfQmBa51CmqrSs2kCfGLGA1ynfYENsxcJq9nsXrb4i17H5BH
 JFkH0g7BUDpeBeLr8gsK3WgfqWwtZsDkltObw9chUD/siK6q/dk/fSIB2Ho0inev7k68Z5
 ZkNI4XOwuEssAVhmwA==
 ---- 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, INSECURE), 'SHA256' or any other hash supported by Crypt::Digest

BEWARE: The $hash_name default is 'SHA1' only for backward compatibility. SHA-1 is vulnerable to practical collision attacks and is not safe for signing messages whose content may be influenced by an attacker. Always pass an explicit hash name such as 'SHA256'. The same applies to "verify_message".

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, INSECURE), '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 -sha256 -sign dsakey.priv.pem -out input.sha256-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.sha256-dsa.sig");
 my $valid = $pkdsa->verify_hash($signature, digest_file("SHA256", "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("SHA256", "input.data"));
 write_rawfile("input.sha256-dsa.sig", $signature);

Verify signature (from commandline):

 openssl dgst -sha256 -verify dsakey.pub.pem -signature input.sha256-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");

SEE ALSO

•

<https://en.wikipedia.org/wiki/Digital_Signature_Algorithm>

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