#!/usr/bin/perl -w

# We expect an input file and a key
$stdinlen = (stat(STDIN))[7];
if($#ARGV != 0 || $stdinlen == 0) {
	print "Usage: crypt.pl file < key > output\n";
	exit(1);
}

# Open the file
open(FILEIO, "<", $ARGV[0]) or die "Can't open file: $!";
$filelen = (stat(FILEIO))[7];

# Read in the key, since we can't seek on STDIN :(
$keylen = ($stdinlen < $filelen) ? $stdinlen : $filelen;
read(STDIN, $key, $keylen);

# Read in the file, XORing each byte 
for($i = 0; $i < $filelen; $i ++) {
	read(FILEIO, $x, 1);
	$x ^= substr($key, $i % $keylen, 1);
	print $x;
}

close(FILEIO);