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Riley Schneider
297
database/perl/vendor/lib/Crypt/DSA.pm
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297
database/perl/vendor/lib/Crypt/DSA.pm
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package Crypt::DSA;
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use 5.006;
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use strict;
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use Digest::SHA1 qw( sha1 );
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use Carp qw( croak );
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use Crypt::DSA::KeyChain;
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use Crypt::DSA::Key;
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use Crypt::DSA::Signature;
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use Crypt::DSA::Util qw( bitsize bin2mp mod_inverse mod_exp makerandom );
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use vars qw( $VERSION );
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BEGIN {
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$VERSION = '1.17';
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}
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sub new {
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my $class = shift;
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my $dsa = bless { @_ }, $class;
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$dsa->{_keychain} = Crypt::DSA::KeyChain->new(@_);
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$dsa;
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}
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sub keygen {
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my $dsa = shift;
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my $key = $dsa->{_keychain}->generate_params(@_);
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$dsa->{_keychain}->generate_keys($key);
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$key;
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}
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sub sign {
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my $dsa = shift;
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my %param = @_;
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my($key, $dgst);
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croak __PACKAGE__, "->sign: Need a Key" unless $key = $param{Key};
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unless ($dgst = $param{Digest}) {
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croak __PACKAGE__, "->sign: Need either Message or Digest"
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unless $param{Message};
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$dgst = sha1($param{Message});
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}
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my $dlen = length $dgst;
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my $i = bitsize($key->q) / 8;
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croak "Data too large for key size"
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if $dlen > $i || $dlen > 50;
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$dsa->_sign_setup($key)
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unless $key->kinv && $key->r;
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my $m = bin2mp($dgst);
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my $xr = ($key->priv_key * $key->r) % $key->q;
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my $s = $xr + $m;
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$s -= $key->q if $s > $key->q;
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$s = ($s * $key->kinv) % $key->q;
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my $sig = Crypt::DSA::Signature->new;
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$sig->r($key->r);
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$sig->s($s);
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$sig;
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}
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sub _sign_setup {
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my $dsa = shift;
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my $key = shift;
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my($k, $r);
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{
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$k = makerandom(Size => bitsize($key->q));
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$k -= $key->q if $k >= $key->q;
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redo if $k == 0;
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}
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$r = mod_exp($key->g, $k, $key->p);
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$r %= $key->q;
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my $kinv = mod_inverse($k, $key->q);
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$key->r($r);
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$key->kinv($kinv);
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}
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sub verify {
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my $dsa = shift;
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my %param = @_;
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my($key, $dgst, $sig);
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croak __PACKAGE__, "->verify: Need a Key" unless $key = $param{Key};
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unless ($dgst = $param{Digest}) {
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croak __PACKAGE__, "->verify: Need either Message or Digest"
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unless $param{Message};
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$dgst = sha1($param{Message});
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}
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croak __PACKAGE__, "->verify: Need a Signature"
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unless $sig = $param{Signature};
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my $u2 = mod_inverse($sig->s, $key->q);
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my $u1 = bin2mp($dgst);
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$u1 = ($u1 * $u2) % $key->q;
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$u2 = ($sig->r * $u2) % $key->q;
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my $t1 = mod_exp($key->g, $u1, $key->p);
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my $t2 = mod_exp($key->pub_key, $u2, $key->p);
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$u1 = ($t1 * $t2) % $key->p;
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$u1 %= $key->q;
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$u1 == $sig->r;
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}
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1;
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__END__
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=pod
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=head1 NAME
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Crypt::DSA - DSA Signatures and Key Generation
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=head1 SYNOPSIS
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use Crypt::DSA;
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my $dsa = Crypt::DSA->new;
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my $key = $dsa->keygen(
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Size => 512,
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Seed => $seed,
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Verbosity => 1
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);
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my $sig = $dsa->sign(
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Message => "foo bar",
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Key => $key
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);
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my $verified = $dsa->verify(
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Message => "foo bar",
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Signature => $sig,
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Key => $key,
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);
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=head1 DESCRIPTION
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I<Crypt::DSA> is an implementation of the DSA (Digital Signature
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Algorithm) signature verification system. The implementation
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itself is pure Perl, although the heavy-duty mathematics underneath
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are provided by the I<Math::Pari> library.
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This package provides DSA signing, signature verification, and key
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generation.
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=head1 USAGE
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The I<Crypt::DSA> public interface is similar to that of
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I<Crypt::RSA>. This was done intentionally.
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=head2 Crypt::DSA->new
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Constructs a new I<Crypt::DSA> object. At the moment this isn't
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particularly useful in itself, other than being the object you
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need to do much else in the system.
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Returns the new object.
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=head2 $key = $dsa->keygen(%arg)
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Generates a new set of DSA keys, including both the public and
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private portions of the key.
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I<%arg> can contain:
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=over 4
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=item * Size
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The size in bits of the I<p> value to generate. The I<q> and
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I<g> values are always 160 bits each.
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This argument is mandatory.
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=item * Seed
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A seed with which I<q> generation will begin. If this seed does
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not lead to a suitable prime, it will be discarded, and a new
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random seed chosen in its place, until a suitable prime can be
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found.
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This is entirely optional, and if not provided a random seed will
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be generated automatically.
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=item * Verbosity
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Should be either 0 or 1. A value of 1 will give you a progress
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meter during I<p> and I<q> generation--this can be useful, since
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the process can be relatively long.
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The default is 0.
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=back
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=head2 $signature = $dsa->sign(%arg)
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Signs a message (or the digest of a message) using the private
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portion of the DSA key and returns the signature.
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The return value--the signature--is a I<Crypt::DSA::Signature>
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object.
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I<%arg> can include:
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=over 4
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=item * Digest
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A digest to be signed. The digest should be 20 bytes in length
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or less.
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You must provide either this argument or I<Message> (see below).
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=item * Key
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The I<Crypt::DSA::Key> object with which the signature will be
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generated. Should contain a private key attribute (I<priv_key>).
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This argument is required.
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=item * Message
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A plaintext message to be signed. If you provide this argument,
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I<sign> will first produce a SHA1 digest of the plaintext, then
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use that as the digest to sign. Thus writing
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my $sign = $dsa->sign(Message => $message, ... );
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is a shorter way of writing
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use Digest::SHA1 qw( sha1 );
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my $sig = $dsa->sign(Digest => sha1( $message ), ... );
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=back
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=head2 $verified = $dsa->verify(%arg)
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Verifies a signature generated with I<sign>. Returns a true
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value on success and false on failure.
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I<%arg> can contain:
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=over 4
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=item * Key
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Key of the signer of the message; a I<Crypt::DSA::Key> object.
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The public portion of the key is used to verify the signature.
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This argument is required.
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=item * Signature
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The signature itself. Should be in the same format as returned
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from I<sign>, a I<Crypt::DSA::Signature> object.
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This argument is required.
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=item * Digest
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The original signed digest whose length is less than or equal to
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20 bytes.
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Either this argument or I<Message> (see below) must be present.
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=item * Message
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As above in I<sign>, the plaintext message that was signed, a
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string of arbitrary length. A SHA1 digest of this message will
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be created and used in the verification process.
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=back
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=head1 TODO
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Add ability to munge format of keys. For example, read/write keys
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from/to key files (SSH key files, etc.), and also write them in
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other formats.
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=head1 SUPPORT
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Bugs should be reported via the CPAN bug tracker at
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L<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Crypt-DSA>
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For other issues, contact the author.
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=head1 AUTHOR
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Benjamin Trott E<lt>ben@sixapart.comE<gt>
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=head1 COPYRIGHT
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Except where otherwise noted,
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Crypt::DSA is Copyright 2006 - 2011 Benjamin Trott.
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Crypt::DSA is free software; you may redistribute it
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and/or modify it under the same terms as Perl itself.
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=cut
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