How to use the Caesar cipher
- Type your message into Input.
- Choose Encode or Decode and set the Shift, the number of places each letter moves. Don't know the shift? Pick Try every shift.
- Copy the result. Whoever reads it decodes with the same shift.
A cipher from ancient Rome
The Roman historian Suetonius described how Julius Caesar wrote confidential letters by replacing each letter with the one three places further on in the alphabet, so A became D. In the same work he says Augustus used a shift of one. The name now covers any shift. With a shift of 3, “Veni, vidi, vici” becomes “Yhql, ylgl, ylfl”.
Encoding by hand
Write the alphabet out, then write it again underneath, starting from the shift. For a shift of 3:
Plain: ABCDEFGHIJKLMNOPQRSTUVWXYZ
Cipher: DEFGHIJKLMNOPQRSTUVWXYZABCFind each letter of your message in the top row and write down the letter below it. Letters near the end wrap around to the start, so X, Y and Z become A, B and C. With only 25 possible keys it’s a good first cipher for learning and for puzzles, not for keeping secrets.