Suppose you and your friends wanted to set up a system of sending secret messages to each other You might say, “Instead of using letters, let’s use numbers.” Each number will stand for a certain letter of the alphabet.

You would then have a code. Cryptography is writing using a secret code. Sometimes the word “cipher” is used instead of code. Did you know that Julius Caesar used a cipher to keep his message secret from enemy eyes? In modern times, ciphers and codes are used by both government and business for important and secret messages.