Recent posts regarding file encryption prompted me to dust off this old thing and recode in perl.

It uses "alleged RC4" which generates numbers 0-255. The RNG stream is XOR'd with the input stream to create the output stream.

The period of ARC4 is about 256**256, there is little chance of being able to reproduce the initial RNG state by brute force. If you lose the key phrase, you are toast.

Needless to say, the perl version is about 1/8 the size of the original C version. :)

#!/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;

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In reply to REAL unbreakable crypto by zude

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