#!/usr/bin/perl
# symmetrical cipher STDIN to STDOUT
use warnings; 
use strict;

@ARGV or die "Usage $0 keyphrase < source > dest\n";
my @key = unpack "C*", "@ARGV";

# init ARC4 state from key
my @s = (0..255); 
my $i=0; 
for (0..255)
{       
  $i+=$key[$_%@key]+$s[$_], $i%=256;
  ($s[$_],$s[$i])=($s[$i],$s[$_]);
}

# do the magic
my $x=0; my $y=0; my $t;
print pack "C*", map          
{
  $x++, $x%=256;
  $y+=$s[$x], $y%=256;
  ($s[$x],$s[$y])=($s[$y],$s[$x]);
  $_^$s[($s[$x]+$s[$y])%256];
} unpack "C*", $t while read STDIN, $t, 32768;