Caesar cipher
The Caesar cipher is one of the oldest known ways to hide a message. According to the historian Suetonius, Julius Caesar used it in his private letters: each letter of the message is replaced by the letter a few places further along the alphabet. With a shift of 3, A becomes D, B becomes E, and Z wraps round to the start and becomes C.
It is a perfect first cipher for the classroom: students get it in a minute, can solve it with pencil and paper and, with a Caesar wheel, decode it without counting on their fingers.
Try it
Type a message, choose the shift and copy the result. You can turn the wheel with the buttons under it or with the arrow keys. Accents are dropped and the result is written in capitals, as classic ciphers are. With the 27-letter alphabet, Ñ counts as a letter of its own, between N and O.
How many places each letter moves: from 0 to 25.
35 of 600 characters
WRPRUURZ ZH RSHQ WKH WUHDVXUH FKHVW
The key
Each letter in the top row is encoded as the letter under it. To decode, go the other way.
| Letter | 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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Becomes | 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 |
Classroom ideas
- Ask your students to decode a clue without telling them the shift: there are only 25 possibilities (26 with Ñ), so they can try them one by one.
- Make the shift part of another puzzle: for example, the number that opens the previous lock.
Printable worksheet
Practise this cipher on paper: a worksheet with the key and two exercises, ready to print or download with its answer key. Open the worksheet