Codebreakers · Mission 1 · Rome, 50 BC

Caesar's Cipher Wheel

3 KEY

Drag the gold wheel to turn it, or use the arrow keys. Outer ring = plaintext, inner ring = ciphertext.

Secret key (shift)
3
A → D Every letter moves 3 places forward.
Message
Ciphertext
The whole alphabet at this key
Crack it: try every key (brute force)

Put a secret message in the Message box. There are only 25 possible keys, so a codebreaker can try them all. Find the line that makes sense, then tap it to set the wheel to that key.

Set the key

Turn the inner wheel until the key letter sits under outer A. The small number under A is the key.

Encrypt

Find each plaintext letter on the outer ring. Write down the inner letter next to it.

Decrypt

Find each ciphertext letter on the inner ring. Write down the outer letter next to it.

It's an algorithm

The same steps repeat for every letter, like a loop in a computer program.