package Crypt::TripleRC4;

use strict;
use vars qw($VERSION @ISA @EXPORT @EXPORT_OK);

require Exporter;

@ISA     = qw(Exporter AutoLoader);
@EXPORT  = qw(TripleRC4);
$VERSION = '0.01';

sub TripleRC4 {
    my ( $key, $text, $mode ) = @_;
    my ( $text1, $text2, $text3 ) = undef;
    my $key2 = _RC4( $key, $key );
    my $key3 = $key2 ^ $key;
    if ( $mode =~ /e/i ) {
        $text1 = _RC4( $key,  $text );
        $text2 = _RC4( $key2, $text1 );
        $text3 = _RC4( $key3, $text2 );
    } elsif ( $mode =~ /d/i ) {
        $text1 = _RC4( $key3, $text );
        $text2 = _RC4( $key2, $text1 );
        $text3 = _RC4( $key,  $text2 );
    } else {
        return undef;
    }
    return $text3;
}

sub _RC4 {
    my $x = 0;
    my $y = 0;

    my $key = shift;
    my @k   = unpack( 'C*', $key );
    my @s   = 0 .. 255;

    for ( $x = 0 ; $x != 256 ; $x++ ) {
        $y = ( $k[ $x % @k ] + $s[$x] + $y ) % 256;
        @s[ $x, $y ] = @s[ $y, $x ];
    }

    $x = $y = 0;

    my $z = undef;

    for ( unpack( 'C*', shift ) ) {
        $x = ( $x + 1 ) % 256;
        $y = ( $s[$x] + $y ) % 256;
        @s[ $x, $y ] = @s[ $y, $x ];
        $z .= pack( 'C', $_ ^= $s[ ( $s[$x] + $s[$y] ) % 256 ] );
    }

    return $z;
}

1;
__END__

=head1 NAME

Crypt::TripleRC4 - Modified perl implementation of the RC4 encryption algorithm

=head1 SYNOPSIS

  use Crypt::TripleRC4;
  $encrypted = TripleRC4( $passphrase, $plaintext, "e" );
  $decrypt = TripleRC4( $passphrase, $encrypted, "d" );

=head1 DESCRIPTION

This differs from standard RC4 in that three keys are used to encrypt the text. KEY1 is the key 
entered by the user.  KEY2 is KEY1 encrypted using itself as the key.  KEY3 is KEY2 ^ KEY1.  
I am uncertain as to what, if any, benefit is provided by this, hence the reason I'm posting 
this to Perlmonks.  The idea for TripleRC4 stems from TripleDES.

=head1 AUTHOR

Kurt Kincaid (sifukurt@yahoo.com)

=head1 SEE ALSO

perl(1), http://www.cypherspace.org, http://www.rsasecurity.com

=cut