package Crypt::OpenPGP::Signature;
use strict;
use warnings;

our $VERSION = '1.21'; # VERSION

use Crypt::OpenPGP::Digest;
use Crypt::OpenPGP::Signature::SubPacket;
use Crypt::OpenPGP::Key::Public;
use Crypt::OpenPGP::Constants qw( DEFAULT_DIGEST );
use parent qw( Crypt::OpenPGP::ErrorHandler );

sub pkt_hdrlen { 2 }

our %KEY_ALG = (
    1 => 'RSA',
    16 => 'ElGamal',
    17 => 'DSA',
);

sub key_id {
    my $sig = shift;
    unless ($sig->{key_id}) {
        my $sp = $sig->find_subpacket(16);
        $sig->{key_id} = $sp->{data};
    }
    $sig->{key_id};
}

sub timestamp {
    my $sig = shift;
    $sig->{version} < 4 ?
        $sig->{timestamp} :
        $sig->find_subpacket(2)->{data};
}

sub digest {
    my $sig = shift;
    Crypt::OpenPGP::Digest->new($sig->{hash_alg});
}

sub find_subpacket {
    my $sig = shift;
    my($type) = @_;
    my @sp = (@{$sig->{subpackets_hashed}}, @{$sig->{subpackets_unhashed}});
    for my $sp (@sp) {
        return $sp if $sp->{type} == $type;
    }
}

sub new {
    my $class = shift;
    my $sig = bless { }, $class;
    $sig->init(@_);
}

sub init {
    my $sig = shift;
    my %param = @_;
    $sig->{subpackets_hashed} = [];
    $sig->{subpackets_unhashed} = [];
    if ((my $obj = $param{Data}) && (my $cert = $param{Key})) {
        $sig->{version} = $param{Version} || 4;
        $sig->{type} = $param{Type} || 0x00;
        $sig->{hash_alg} = $param{Digest} ? $param{Digest} :
            $sig->{version} == 4 ? DEFAULT_DIGEST : 1;
        $sig->{pk_alg} = $cert->key->alg_id;
        if ($sig->{version} < 4) {
            $sig->{timestamp} = time;
            $sig->{key_id} = $cert->key_id;
            $sig->{hash_len} = 5;
        }
        else {
            my $sp = Crypt::OpenPGP::Signature::SubPacket->new;
            $sp->{type} = 2;
            $sp->{data} = time;
            push @{ $sig->{subpackets_hashed} }, $sp;
            $sp = Crypt::OpenPGP::Signature::SubPacket->new;
            $sp->{type} = 16;
            $sp->{data} = $cert->key_id;
            push @{ $sig->{subpackets_unhashed} }, $sp;
        }
        my $hash = $sig->hash_data(ref($obj) eq 'ARRAY' ? @$obj : $obj);
        $sig->{chk} = substr $hash, 0, 2;
        my $sig_data = $cert->key->sign($hash,
            Crypt::OpenPGP::Digest->alg($sig->{hash_alg}));
        my @sig = $cert->key->sig_props;
        for my $e (@sig) {
            $sig->{$e} = $sig_data->{$e};
        }
    }
    $sig;
}

sub sig_trailer {
    my $sig = shift;
    my $buf = Crypt::OpenPGP::Buffer->new;
    if ($sig->{version} < 4) {
        $buf->put_int8($sig->{type});
        $buf->put_int32($sig->{timestamp});
    }
    else {
        $buf->put_int8($sig->{version});
        $buf->put_int8($sig->{type});
        $buf->put_int8($sig->{pk_alg});
        $buf->put_int8($sig->{hash_alg});
        my $sp_data = $sig->_save_subpackets('hashed');
        $buf->put_int16(defined $sp_data ? length($sp_data) : 0);
        $buf->put_bytes($sp_data) if $sp_data;
        my $len = $buf->length;
        $buf->put_int8($sig->{version});
        $buf->put_int8(0xff);
        $buf->put_int32($len);
    }
    $buf->bytes;
}

sub parse {
    my $class = shift;
    my($buf) = @_;
    my $sig = $class->new;

    $sig->{version} = $buf->get_int8;
    if ($sig->{version} < 4) {
        $sig->{sig_data} = $buf->bytes($buf->offset+1, 5);
        $sig->{hash_len} = $buf->get_int8;
        return $class->error("Hash len $sig->{hash_len} != 5")
            unless $sig->{hash_len} == 5;
        $sig->{type} = $buf->get_int8;
        $sig->{timestamp} = $buf->get_int32;
        $sig->{key_id} = $buf->get_bytes(8);
        $sig->{pk_alg} = $buf->get_int8;
        $sig->{hash_alg} = $buf->get_int8;
    }
    else {
        $sig->{sig_data} = $buf->bytes($buf->offset-1, 6);
        $sig->{type} = $buf->get_int8;
        $sig->{pk_alg} = $buf->get_int8;
        $sig->{hash_alg} = $buf->get_int8;
        for my $h (qw( hashed unhashed )) {
            my $subpack_len = $buf->get_int16;
            my $sp_buf = $buf->extract($subpack_len);
            $sig->{sig_data} .= $sp_buf->bytes if $h eq 'hashed';
            while ($sp_buf->offset < $sp_buf->length) {
                my $len = $sp_buf->get_int8;
                if ($len >= 192 && $len < 255) {
                    my $len2 = $sp_buf->get_int8;
                    $len = (($len-192) << 8) + $len2 + 192;
                } elsif ($len == 255) {
                    $len = $sp_buf->get_int32;
                }
                my $this_buf = $sp_buf->extract($len);
                my $sp = Crypt::OpenPGP::Signature::SubPacket->parse($this_buf);
                push @{ $sig->{"subpackets_$h"} }, $sp;
            }
        }
    }
    our %KEY_ALG;
    eval require Crypt::DSA::GMP if $KEY_ALG{$sig->{pk_alg}} eq 'DSA'; 
    $sig->{chk} = $buf->get_bytes(2);
    ## XXX should be Crypt::OpenPGP::Signature->new($sig->{pk_alg})?
    my $key = Crypt::OpenPGP::Key::Public->new($sig->{pk_alg})
        or return $class->error(Crypt::OpenPGP::Key::Public->errstr);
    my @sig = $key->sig_props;
    for my $e (@sig) {
        $sig->{$e} = $buf->get_mp_int;
    }
    $sig;
}

sub save {
    my $sig = shift;
    my $buf = Crypt::OpenPGP::Buffer->new;
    $buf->put_int8($sig->{version});
    if ($sig->{version} < 4) {
        $buf->put_int8($sig->{hash_len});
        $buf->put_int8($sig->{type});
        $buf->put_int32($sig->{timestamp});
        $buf->put_bytes($sig->{key_id}, 8);
        $buf->put_int8($sig->{pk_alg});
        $buf->put_int8($sig->{hash_alg});
    }
    else {
        $buf->put_int8($sig->{type});
        $buf->put_int8($sig->{pk_alg});
        $buf->put_int8($sig->{hash_alg});
        for my $h (qw( hashed unhashed )) {
            my $sp_data = $sig->_save_subpackets($h);
            $buf->put_int16(defined $sp_data ? length($sp_data) : 0);
            $buf->put_bytes($sp_data) if $sp_data;
        }
    }
    $buf->put_bytes($sig->{chk}, 2);
    ## XXX should be Crypt::OpenPGP::Signature->new($sig->{pk_alg})?
    my $key = Crypt::OpenPGP::Key::Public->new($sig->{pk_alg});
    my @sig = $key->sig_props;
    for my $e (@sig) {
        $buf->put_mp_int($sig->{$e});
    }
    $buf->bytes;
}

sub _save_subpackets {
    my $sig = shift;
    my($h) = @_;
    my @sp;
    return unless $sig->{"subpackets_$h"} &&
        (@sp = @{ $sig->{"subpackets_$h"} });
    my $sp_buf = Crypt::OpenPGP::Buffer->new;
    for my $sp (@sp) {
        my $data = $sp->save;
        my $len = length $data;
        if ($len < 192) {
            $sp_buf->put_int8($len);
        } elsif ($len < 8384) {
            $len -= 192;
            $sp_buf->put_int8( int($len / 256) + 192 );
            $sp_buf->put_int8( $len % 256 );
        } else {
            $sp_buf->put_int8(255);
            $sp_buf->put_int32($len);
        }
        $sp_buf->put_bytes($data);
    }
    $sp_buf->bytes;
}

sub hash_data {
    my $sig = shift;
    my $buf = Crypt::OpenPGP::Buffer->new;
    my $type = ref($_[0]);
    if ($type eq 'Crypt::OpenPGP::Certificate') {
        my $cert = shift;
        $buf->put_int8(0x99);
        my $pk = $cert->public_cert->save;
        $buf->put_int16(length $pk);
        $buf->put_bytes($pk);

        if (@_) {
            if (ref($_[0]) eq 'Crypt::OpenPGP::UserID') {
                my $uid = shift;
                my $ud = $uid->save;
                if ($sig->{version} >= 4) {
                    $buf->put_int8(0xb4);
                    $buf->put_int32(length $ud);
                }
                $buf->put_bytes($ud);
            }
            elsif (ref($_[0]) eq 'Crypt::OpenPGP::Certificate') {
                my $subcert = shift;
                $buf->put_int8(0x99);
                my $k = $subcert->public_cert->save;
                $buf->put_int16(length $k);
                $buf->put_bytes($k);
            }
        }
    }
    elsif ($type eq 'Crypt::OpenPGP::Plaintext') {
        my $pt = shift;
        my $data = $pt->data;
        if ($pt->mode eq 't') {
            require Crypt::OpenPGP::Util;
            $buf->put_bytes(Crypt::OpenPGP::Util::canonical_text($data));
        }
        else {
            $buf->put_bytes($data);
        }
    }

    $buf->put_bytes($sig->sig_trailer);

    my $hash = Crypt::OpenPGP::Digest->new($sig->{hash_alg}) or
        return $sig->error( Crypt::OpenPGP::Digest->errstr );
    $hash->hash($buf->bytes);
}

1;
__END__

=head1 NAME

Crypt::OpenPGP::Signature - Signature packet

=head1 SYNOPSIS

    use Crypt::OpenPGP::Signature;

    my $cert = Crypt::OpenPGP::Certificate->new;
    my $plaintext = 'foo bar';

    my $sig = Crypt::OpenPGP::Signature->new(
        Key  => $cert,
        Data => $plaintext,
    );
    my $serialized = $sig->save;

=head1 DESCRIPTION

I<Crypt::OpenPGP::Signature> implements PGP signature packets and
provides functionality for hashing PGP packets to obtain message
digests; these digests are then signed by the secret key to form a
signature.

I<Crypt::OpenPGP::Signature> reads and writes both version 3 and version
4 signatures, along with the signature subpackets found in version 4
(see I<Crypt::OpenPGP::Signature::SubPacket>).

=head1 USAGE

=head2 Crypt::OpenPGP::Signature->new( %arg )

Creates a new signature packet object and returns that object. If
there are no arguments in I<%arg>, the object is created empty; this is
used, for example, in I<parse> (below), to create an empty packet which is
then filled from the data in the buffer.

If you wish to initialize a non-empty object, I<%arg> can contain:

=over 4

=item * Data

A PGP packet object of some kind. Currently the two supported objects
are I<Crypt::OpenPGP::Certificate> objects, to create self-signatures
for keyrings, and I<Crypt::OpenPGP::Plaintext> objects, for signatures
on blocks of data.

This argument is required (for a non-empty packet).

=item * Key

A secret-key certificate that can be used to sign the data. In other
words an object of type I<Crypt::OpenPGP::Certificate> that holds
a secret key.

This argument is required.

=item * Version

The packet format version of the signature. Valid values are either
C<3> or C<4>; version C<4> signatures are the default, but will be
incompatible with older PGP implementations; for example, PGP2 will
only read version 3 signatures; PGP5 can read version 4 signatures,
but only on signatures of data packets (not on key signatures).

This argument is optional; the default is version 4.

=item * Type

Specifies the type of signature (data, key, etc.). Valid values can
be found in the OpenPGP RFC, section 5.2.1.

This argument is optional; the default is C<0x00>, signature of a
binary document.

=item * Digest

The digest algorithm to use when generating the digest of the data
to be signed. See the documentation for I<Crypt::OpenPGP::Digest>
for a list of valid values.

This argument is optional; the default is C<SHA1>.

=back

=head2 $sig->save

Serializes the signature packet and returns a string of octets.

=head2 Crypt::OpenPGP::Signature->parse($buffer)

Given I<$buffer>, a I<Crypt::OpenPGP::Buffer> object holding (or
with offset pointing to) a signature packet, returns a new
I<Crypt::OpenPGP::Signature> object, initialized with the signature
data in the buffer.

=head2 $sig->hash_data(@data)

Prepares a digital hash of the packets in I<@data>; the hashing method
depends on the type of packets in I<@data>, and the hashing algorithm used
depends on the algorithm associated with the I<Crypt::OpenPGP::Signature>
object I<$sig>. This digital hash is then signed to produce the signature
itself.

You generally do not need to use this method unless you have not passed in
the I<Data> parameter to I<new> (above).

There are two possible packet types that can be included in I<@data>:

=over 4

=item * Key Certificate and User ID

An OpenPGP keyblock contains a key certificate and a signature of the
public key and user ID made by the secret key. This is called a
self-signature. To produce a self-signature, I<@data> should contain two
packet objects: a I<Crypt::OpenPGP::Certificate> object and a
I<Crypt::OpenPGP::UserID> object. For example:

    my $hash = $sig->hash_data($cert, $id)
        or die $sig->errstr;

=item * Plaintext

To sign a piece of plaintext, pass in a I<Crypt::OpenPGP::Plaintext> object.
This is a standard OpenPGP signature.

    my $pt = Crypt::OpenPGP::Plaintext->new( Data => 'foo bar' );
    my $hash = $sig->hash_data($pt)
        or die $sig->errstr;

=back

=head2 $sig->key_id

Returns the ID of the key that created the signature.

=head2 $sig->timestamp

Returns the time that the signature was created in Unix epoch time (seconds
since 1970).

=head2 $sig->digest

Returns a Crypt::OpenPGP::Digest object representing the digest algorithm
used by the signature.

=head1 AUTHOR & COPYRIGHTS

Please see the Crypt::OpenPGP manpage for author, copyright, and
license information.

=cut
