package Crypt::RSA::Primitives;
use strict;
use warnings;

## Crypt::RSA::Primitives -- Cryptography and encoding primitives
##                           used by Crypt::RSA.
##
## Copyright (c) 2001, Vipul Ved Prakash.  All rights reserved.
## This code is free software; you can redistribute it and/or modify
## it under the same terms as Perl itself.

use base 'Crypt::RSA::Errorhandler';
use Crypt::RSA::Debug qw(debug);
use Math::BigInt try => 'GMP, Pari';
use Carp;

sub new {
    return bless {}, shift;
}


sub core_encrypt {

    # procedure:
    # c = (m ** e) mod n

    my ($self, %params) = @_;
    my $key = $params{Key};
    $self->error ("Bad key.", \%params, $key) unless $key->check();
    my $plaintext = (defined $params{Message}) ? $params{Message} : $params{Plaintext};
    $plaintext = Math::BigInt->new("$plaintext") if ref($plaintext) ne 'Math::BigInt';
    debug ("pt == $plaintext");

    my $e = $key->e;
    my $n = $key->n;
    return $self->error ("Numeric representation of plaintext is out of bound.",
                          \$plaintext, $key, \%params) if $plaintext > $n;
    my $c = $plaintext->bmodpow($e, $n);
    debug ("ct == $c");
    $n = undef;
    $e = undef;
    return $c;
}


sub core_decrypt {

    # procedure:
    # p = (c ** d) mod n

    my ($self, %params) = @_;
    my $key = $params{Key};
    $self->error ("Bad key.") unless $key->check();

    my $cyphertext = defined $params{Cyphertext} ? $params{Cyphertext} : $params{Ciphertext};
    $cyphertext = Math::BigInt->new("$cyphertext") if ref($cyphertext) ne 'Math::BigInt';
    my $n = $key->n;
    my $d = $key->d;
    return $self->error ("Decryption error.") if $cyphertext > $n;

    my $pt;
    if ($key->p && $key->q) {
        # Garner's CRT algorithm
        my $p = $key->p;
        my $q = $key->q;
        $key->u ($p->copy->bmodinv($q)) unless defined $key->u;
        $key->dp($d % ($p-1)          ) unless defined $key->dp;
        $key->dq($d % ($q-1)          ) unless defined $key->dq;
        my $u  = $key->u;
        my $dp = $key->dp;
        my $dq = $key->dq;
        my $p2 = ($cyphertext % $p)->bmodpow($dp, $p);
        my $q2 = ($cyphertext % $q)->bmodpow($dq, $q);
        $pt = $p2 + ($p * ((($q2 - $p2) * $u) % $q));
    }
    else {
        $pt = $cyphertext->copy->bmodpow($d, $n);
    }

    debug ("ct == $cyphertext");
    debug ("pt == $pt");
    return $pt;
}


sub core_sign {

    my ($self, %params) = @_;
    $params{Cyphertext} = $params{Message} || $params{Plaintext};
    return $self->core_decrypt (%params);

}


sub core_verify {

    my ($self, %params) = @_;
    $params{Plaintext} = $params{Signature};
    return $self->core_encrypt (%params);

}


1;

=head1 NAME

Crypt::RSA::Primitives - RSA encryption, decryption, signature and verification primitives.

=head1 SYNOPSIS

    my $prim = new Crypt::RSA::Primitives;
    my $ctxt = $prim->core_encrypt (Key => $key, Plaintext => $string);
    my $ptxt = $prim->core_decrypt (Key => $key, Cyphertext => $ctxt);
    my $sign = $prim->core_sign    (Key => $key, Message => $string);
    my $vrfy = $prim->core_verify  (Key => $key, Signature => $sig);

=head1 DESCRIPTION

This module implements RSA encryption, decryption, signature and
verification primitives. These primitives should only be used in the
context of an encryption or signing scheme. See Crypt::RSA::ES::OAEP(3),
and Crypt::RSA::SS::PSS(3) for the implementation of two such schemes.

=head1 ERROR HANDLING

See B<ERROR HANDLING> in Crypt::RSA(3) manpage.

=head1 AUTHOR

Vipul Ved Prakash, E<lt>mail@vipul.netE<gt>

=head1 SEE ALSO

Crypt::RSA(3), Crypt::RSA::Key(3), Crypt::RSA::ES::OAEP(3),
Crypt::RSA::SS::PSS(3)

=cut