File Coverage

blib/lib/Crypt/DSA.pm

Criterion	Covered	Total	%
statement	85	85	100.0
branch	10	20	50.0
condition	1	3	33.3
subroutine	15	15	100.0
pod	4	4	100.0
total	115	127	90.5

package Crypt::DSA;

use 5.006;
use strict;
use warnings;
use Digest::SHA qw( sha1 );
use Carp qw( croak );
use Crypt::DSA::KeyChain;
use Crypt::DSA::Key;
use Crypt::DSA::Signature;
use Crypt::DSA::Util qw( bitsize bin2mp mod_inverse mod_exp makerandom randombelow );

our $VERSION = '1.24'; #VERSION

use vars qw( $VERSION );

sub new {
    my $class = shift;
    my $dsa = bless { @_ }, $class;
    $dsa->{_keychain} = Crypt::DSA::KeyChain->new(@_);
    $dsa;
}

sub keygen {
    my $dsa = shift;
    my $key = $dsa->{_keychain}->generate_params(@_);
    $dsa->{_keychain}->generate_keys($key);
    $key;
}

sub sign {
    my $dsa = shift;
    my %param = @_;
    my($key, $dgst);
    croak __PACKAGE__, "->sign: Need a Key" unless $key = $param{Key};
    unless ($dgst = $param{Digest}) {
        croak __PACKAGE__, "->sign: Need either Message or Digest"
            unless $param{Message};
        $dgst = sha1($param{Message});
    }
    my $dlen = length $dgst;

    my $i = bitsize($key->q) / 8;
    croak "Data too large for key size"
        if $dlen > $i || $dlen > 50;

    # SECURITY: a DSA nonce (k) must NEVER be reused across signatures;
    # two signatures sharing k disclose the private key. Always generate
    # fresh r/kinv per signature -- do NOT reuse any values cached on the
    # Key object from a previous sign().
    $dsa->_sign_setup($key);

    my $m = bin2mp($dgst);
    my $xr = ($key->priv_key * $key->r) % $key->q;
    my $s = $xr + $m;
    $s -= $key->q if $s > $key->q;
    $s = ($s * $key->kinv) % $key->q;

    my $sig = Crypt::DSA::Signature->new;
    $sig->r($key->r);
    $sig->s($s);
    $sig;
}

sub _sign_setup {
    my $dsa = shift;
    my $key = shift;
    my($k, $r);
    {
        # Nonce must be uniform in [1, q-1].  Do NOT use makerandom()
        # (it forces the high bit, which biases the nonce after folding).
        $k = randombelow($key->q);
        redo if $k == 0;
    }
    $r = mod_exp($key->g, $k, $key->p);
    $r %= $key->q;
    my $kinv = mod_inverse($k, $key->q);
    $key->r($r);
    $key->kinv($kinv);
}

sub verify {
    my $dsa = shift;
    my %param = @_;
    my($key, $dgst, $sig);
    croak __PACKAGE__, "->verify: Need a Key" unless $key = $param{Key};
    unless ($dgst = $param{Digest}) {
        croak __PACKAGE__, "->verify: Need either Message or Digest"
            unless $param{Message};
        $dgst = sha1($param{Message});
    }
    croak __PACKAGE__, "->verify: Need a Signature"
        unless $sig = $param{Signature};
    my $u2 = mod_inverse($sig->s, $key->q);
    my $u1 = bin2mp($dgst);
    $u1 = ($u1 * $u2) % $key->q;
    $u2 = ($sig->r * $u2) % $key->q;
    my $t1 = mod_exp($key->g, $u1, $key->p);
    my $t2 = mod_exp($key->pub_key, $u2, $key->p);
    $u1 = ($t1 * $t2) % $key->p;
    $u1 %= $key->q;
    $u1 == $sig->r;
}

1;

__END__