Xor against a shared secret key is a common approach to lightweight encryption. It is not secure. With a true random key of length greater than the message length it does become more secure.

my $str = 'hello world!';
my $key = 'just another perl hacker';

my $encoded = xor_encode($str,$key);
my $decoded = xor_encode($encoded,$key);
print "$encoded\n$decoded\n";

sub xor_encode {
    my ($str, $key) = @_;
    my $enc_str = '';
    for my $char (split //, $str){
        my $decode = chop $key;
        $enc_str .= chr(ord($char) ^ ord($decode));
        $key = $decode . $key;
    }
   return $enc_str;
}
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