Crypt::RSA::ES::OAEP - Plaintext-aware encryption with RSA.

    my $oaep = new Crypt::RSA::ES::OAEP; 

    my $ct = $oaep->encrypt( Key => $key, Message => $message ) || 
                die $oaep->errstr; 

    my $pt = $oaep->decrypt( Key => $key, Cyphertext => $ct )   || 
                die $oaep->errstr; 

#!/usr/bin/perl -sw
##
## Crypt::RSA::ES::OAEP 
##
## 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.
##
## $Id: OAEP.pm,v 1.24 2001/06/22 23:27:37 vipul Exp $

package Crypt::RSA::ES::OAEP; 
use strict;
use base 'Crypt::RSA::Errorhandler';
use Crypt::Random          qw(makerandom_octet);
use Crypt::RSA::DataFormat qw(bitsize os2ip i2osp octet_xor mgf1 octet_len);
use Crypt::RSA::Primitives;
use Crypt::RSA::Debug      qw(debug);
use Digest::SHA1           qw(sha1);
use Math::Pari             qw(floor);
use Sort::Versions         qw(versioncmp);
use Carp;

$Crypt::RSA::ES::OAEP::VERSION = '1.99';

sub new { 
    my ($class, %params) = @_;
    my $self = bless { primitives => new Crypt::RSA::Primitives, 
                       P          => "",
                       hlen       => 20,
                       VERSION    => $Crypt::RSA::ES::OAEP::VERSION,
                      }, $class;
    if ($params{Version}) { 
        if (versioncmp($params{Version}, '1.15') == -1) { 
            $$self{P} = "Crypt::RSA"; 
            $$self{VERSION} = $params{Version};
        } elsif (versioncmp($params{Version}, $$self{VERSION}) == 1) { 
            croak "Required version ($params{Version}) greater than installed version ($$self{VERSION}) of $class.\n";
        }
    }
    return $self;
}


sub encrypt { 
    my ($self, %params) = @_; 
    my $key = $params{Key}; my $M = $params{Message} || $params{Plaintext};
    return $self->error ("Missing Message or Plaintext parameter", \$key, \%params) unless $M;
    return $self->error ($key->errstr, \$M, $key, \%params) unless $key->check;
    my $k = octet_len ($key->n);  debug ("octet_len of modulus: $k");
    my $em = $self->encode ($M, $self->{P}, $k-1) || 
        return $self->error ($self->errstr, \$M, $key, \%params);
    my $m = os2ip ($em);
    my $c = $self->{primitives}->core_encrypt ( Plaintext => $m, Key => $key );
    my $ec = i2osp ($c, $k);  debug ("ec: $ec");
    return $ec;
}    


sub decrypt { 
    my ($self, %params) = @_;
    my $key = $params{Key}; my $C = $params{Cyphertext} || $params{Ciphertext}; 
    return $self->error ("Missing Cyphertext or Ciphertext parameter", \$key, \%params) unless $C;
    return $self->error ($key->errstr, $key, \%params) unless $key->check;
    my $k = octet_len ($key->n);  
    my $c = os2ip ($C);
    if (bitsize($c) > bitsize($key->n)) { 
        return $self->error ("Decryption error.", $key, \%params) 
    }
    my $m = $self->{primitives}->core_decrypt (Cyphertext => $c, Key => $key) || 
        return $self->error ("Decryption error.", $key, \%params);
    my $em = i2osp ($m, $k-1) || 
        return $self->error ("Decryption error.", $key, \%params);
    my $M; $self->errstrrst;  # reset the errstr
    unless ($M = $self->decode ($em, $$self{P})) { 
        return $self->error ("Decryption error.", $key, \%params) if $self->errstr();
        return $M;
    } 
    return $M;
} 


sub encode { 
    my ($self, $M, $P, $emlen) = @_; 
    my $hlen = $$self{hlen};
    my $mlen = length($M);
    return $self->error ("Message too long.", \$P, \$M) if $mlen > $emlen-(2*$hlen)-1;
    my ($PS, $pslen) = ("", 0);
    if ($pslen = $emlen-(2*$hlen+1+$mlen)) { 
        $PS = chr(0)x$pslen;
    }
    my $phash = $self->hash ($P);
    my $db = $phash . $PS . chr(1) . $M; 
    my $seed = makerandom_octet (Length => $hlen);
    my $dbmask = $self->mgf ($seed, $emlen-$hlen);
    my $maskeddb = octet_xor ($db, $dbmask);
    my $seedmask = $self->mgf ($maskeddb, $hlen);
    my $maskedseed = octet_xor ($seed, $seedmask);
    my $em = $maskedseed . $maskeddb;

    debug ("emlen == $emlen");
    debug ("M == $M [" . length($M) . "]"); 
    debug ("PS == $PS [$pslen]"); 
    debug ("phash == $phash [" . length($phash) . "]"); 
    debug ("seed == $seed [" . length($seed) . "]"); 
    debug ("seedmask == $seedmask [" . length($seedmask) . "]"); 
    debug ("db == $db [" . length($db) . "]"); 
    debug ("dbmask == $dbmask [" . length($dbmask) . "]"); 
    debug ("maskeddb == $maskeddb [" . length($maskeddb) . "]"); 
    debug ("em == $em [" . length($em) . "]"); 

    return $em;
}


sub decode { 
    my ($self, $em, $P) = @_; 
    my $hlen = $$self{hlen};

    debug ("P == $P");
    return $self->error ("Decoding error.", \$P) if length($em) < 2*$hlen+1;
    my $maskedseed = substr $em, 0, $hlen; 
    my $maskeddb = substr $em, $hlen; 
    my $seedmask = $self->mgf ($maskeddb, $hlen);
    my $seed = octet_xor ($maskedseed, $seedmask);
    my $dbmask = $self->mgf ($seed, length($em) - $hlen);
    my $db = octet_xor ($maskeddb, $dbmask); 
    my $phash = $self->hash ($P); 

    debug ("em == $em [" . length($em) . "]"); 
    debug ("phash == $phash [" . length($phash) . "]"); 
    debug ("seed == $seed [" . length($seed) . "]"); 
    debug ("seedmask == $seedmask [" . length($seedmask) . "]"); 
    debug ("maskedseed == $maskedseed [" . length($maskedseed) . "]"); 
    debug ("db == $db [" . length($db) . "]"); 
    debug ("maskeddb == $maskeddb [" . length($maskeddb) . "]"); 
    debug ("dbmask == $dbmask [" . length($dbmask) . "]"); 

    my ($phashorig) = substr $db, 0, $hlen;
    debug ("phashorig == $phashorig [" . length($phashorig) . "]"); 
    return $self->error ("Decoding error.", \$P) unless $phashorig eq $phash; 
    $db = substr $db, $hlen;
    my ($chr0, $chr1) = (chr(0), chr(1));
    my ($ps, $m);
    debug ("db == $db [" . length($db) . "]"); 
    unless ( ($ps, undef, $m) = $db =~ /^($chr0*)($chr1)(.*)$/s ) { 
        return $self->error ("Decoding error.", \$P);
    } 

    return $m;
}


sub hash { 
    my ($self, $data) = @_;
    return sha1 ($data);
}


sub mgf {
    my ($self, @data) = @_;
    return mgf1 (@data);
}


sub encryptblock { 
    my ($self, %params) = @_;
    return octet_len ($params{Key}->n) - 42;
} 


sub decryptblock { 
    my ($self, %params) = @_;
    return octet_len ($params{Key}->n);
}


# should be able to call this as a class method.
sub version {
    my $self = shift;
    return $self->{VERSION};
}


1;