Computer experts use codes and encryption to protect sensitive data and to thwart cyberspies. Only those who are supposed to have access to the data know the key to unlock the codes. You can use codes, too, to send a secret message to a friend. Here are four fun ways to encode your words. Be sure your friend knows the key to unlock the message. As a bonus, we’ve included a fun way to define an easy-to-memorize secure digital password.