Julius Caesar is said to have shifted every letter of his military letters by three places so that a captured messenger could not read them. That idea, and a few relatives of it, are collected here. Pick a cipher, type or paste your text, and the encoded or decoded result appears while you type. These ciphers are not secure by modern standards, but they are perfect for puzzles, geocaching, classroom exercises and a bit of fun.
Use it in three steps
- Choose the Cipher and whether you want to Encode or Decode.
- Set the shift for the Caesar cipher or the key word for Vigenère, then type or paste your text.
- Read the result in the second box and use Copy to take it with you.
The four ciphers
- Caesar cipher: every letter moves forward by a fixed number of places, from 1 to 25. A shift of 3 turns HELLO into KHOOR.
- ROT13: a Caesar cipher with a shift of 13. Because the alphabet has 26 letters, the same step encodes and decodes.
- Atbash: the alphabet is mirrored, so A becomes Z and B becomes Y. Like ROT13, applying it twice restores the text.
- Vigenère: a key word decides the shift of each letter, which makes simple letter counting much less useful than with a single shift.
Solving an unknown message
If you know a text was written with a Caesar cipher but not the shift, open the list of all 25 shifts. There are only 25 possibilities, so one of the lines will be readable. Click it and the shift is applied to the main box. Letters keep their case, and everything that is not a letter from A to Z, including digits, spaces and punctuation, passes through unchanged. Accented letters are left as they are.
Private by design
The calculation happens in your browser and your text is never sent anywhere. Do not rely on these ciphers to protect anything important, because they can be broken in seconds. For real secrets use proper encryption.