Before I begin please let me state that I am doing this for learning purposes, and am well aware of the weakness of XOR encryption. That said, I am having a hell of a time getting a simple XOR routine to work. Here is the code that I have written so far: 
#!/usr/bin/perl

use strict;

if(@ARGV < 3) {
    print "Usage: $0 <key> <input file> <output file>\n";
    exit(0);
}

my $key = $ARGV[0];
open(IN, $ARGV[1]) or die "Can't open infile";
open(OUT, ">$ARGV[2]") or die "Can't open outfile";

my $kp = 0;
while(<IN>) {
    for my $i (0..length($_)) {
    if($kp > length($key)) {
        $kp = 0;
    }

    my $kc = substr($key, $kp++, 1);
    my $char = substr($_, $i, 1);
    
    $char ^= $kc;
    print OUT $char;
    }
}

close(IN);
close(OUT);

[download]
Seems simple enough, but when I encrypt a file and then attempt to de-crypt it with the same key *some* of the file decrypts correctly, but most of it is garbage. A realativly simple task in C, this has had me beating my head against a wall for some time. I'm not exactly a perl kung-fu master, so if anyone has any insight as to what I might be doing wrong, I'd greatly appreciate hearing it.

In reply to xor encrypt-decrypt routine by j0e

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