Given that you can have an industrial strength fence for essentially the same price as a decorative ROT13 one why not just:

use Crypt::Blowfish;
use Crypt::CBC;

$KEY = 'GNUisnotUnix';  # Blowfish will take 56 bytes (448 bits) of ke
+y
my $cipher = new Crypt::CBC( $KEY, 'Blowfish' );

my $enc = encrypt('Hello World');
my $dec = decrypt($enc);
print "$enc\n$dec\n";

sub decrypt { defined $_[0] ? $cipher->decrypt_hex($_[0]) : '' }
sub encrypt { defined $_[0] ? $cipher->encrypt_hex($_[0]) : '' }
[download]

cheers

tachyon

s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print