Caesar and Vigenère cipher
Encode messages with Julius Caesar’s cipher, ROT13, ROT47 or Vigenère, and decrypt texts even without the key: we try all 25 shifts and rank the results by how closely each one resembles real text in your language.
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Decrypt without the key (frequency analysis)
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How to use
- 1Choose the method: Caesar, ROT13, ROT47 or Vigenère.
- 2Pick encrypt or decrypt and set the shift or the key.
- 3Type the message: the result appears instantly.
- 4If you do not know the key, open “Decrypt without the key” and pick the most likely solution.
Use cases
- Solve puzzles, escape rooms and treasure hunts.
- Teach classical cryptography in math or computer science lessons.
- Hide spoilers on forums with ROT13.
- Practice cryptography CTF challenges.
Frequently asked questions
What is the Caesar cipher?
A substitution cipher that shifts each letter a fixed number of positions in the alphabet. With a shift of 3, A becomes D and B becomes E. Julius Caesar used it for military messages.
Is the Caesar cipher secure?
No. There are only 25 possible keys in the Latin alphabet, so it is broken in seconds by trying them all, as this tool does. Use it for games and learning, never to protect real information.
What is the difference between ROT13 and ROT47?
ROT13 is a Caesar shift of 13 that only affects letters and is its own inverse. ROT47 rotates the 94 printable ASCII characters, so it also transforms numbers and symbols.
How does Vigenère work?
It uses a keyword: each letter of the message is shifted by the matching letter of the repeated key. It resists frequency analysis much better than Caesar, although statistical methods can still break it.