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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);
    }