The earliest recorded use of Cryptography for a practical, military purpose comes from the times when the Romans walked the earth, over two thousand years ago. During war, the commander of the Roman army, Julius Caesar, had a problem. He needed to figure out how to communicate with his troops, but make it so that if the enemy intercepted his men, they couldn’t understand the message. To do this, Caesar thought about it, and then came up with a variation on what is now called the substitution cipher. Simply, he shifted the position of letters by three, substituting the resulting letter for the original.

Here is a guide. To use it, find the letter you want to encrypt on the top row. Then, trace down to the bottom row and substitute the letter you find.

Original: ABCDEFGHIJKLMNOPQRSTUVWXYZ
                  becomes
Cipher:   XYZABCDEFGHIJKLMNOPQRSTUVW

For example, the message "ET TU, BRUTE", would become "HW WX, EUXWH".

If you want more fun, check out the interactive substitution cipher applet, and put the cipher key above in for "CipherCode." Then, you can automatically encrypt and decrypt with the Julius Caesar Cipher.

By today’s standards (even last century’s standards), Julius Caesar’s messages were not safe at all. Using modern computer technology, messages encrypted with the Caesar Cipher can be forcibly decoded in a matter of milliseconds.