Secret Codes: How Kids Can Hide a Message

Long ago, a Roman general named Julius Caesar needed to send messages to his soldiers. If an enemy caught the message, he didn't want them to read it! So Caesar shifted every letter a few spots down the alphabet. A became D, B became E, and so on. His soldiers knew the trick, so they could read it, but enemies just saw jumbled letters. That trick is over 2,000 years old, and it still works today. Making and breaking secret codes is called cryptography, and you are about to learn how to do it yourself.

- Why people have hidden messages for thousands of years - How a shift code (like Caesar used) turns words into secret letters - Key words: code, cipher, encrypt, decrypt - How to write and solve your own secret message

People hide messages when they want only certain people to understand them. A general hides battle plans from enemies. A kid might hide a note so a little brother can't read a diary. A company hides passwords so strangers can't get into your bank account online. The hidden message is called a cipher. Turning a normal message into a cipher is called encrypting it. Turning the cipher back into the normal message is called decrypting it.

Here is the exact trick Caesar used, called a shift code. Pick a number, let's use 3. Write out the alphabet, then write it again starting 3 letters later: Normal: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Shifted: D E F G H I J K L M N O P Q R S T U V W X Y Z A B C To encrypt the word CAT: C becomes F, A becomes D, T becomes W. So CAT turns into FDW. To decrypt FDW back into CAT, you just shift backward 3 letters instead.