Caesar / ROT13 / Vigenère / Atbash Cipher
Encrypt or decrypt text with four classic substitution ciphers — Caesar shift, ROT13, Vigenère keyword, Atbash mirror.
How to use
- Pick a cipher and (for Caesar/Vigenère) choose encode or decode.
- Type or paste the text. For Caesar, drag the shift slider; for Vigenère, type the key.
- Output updates live. The brute-force panel below tries all 26 Caesar shifts when you're trying to crack a message.
About this tool
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Four classical letter ciphers in one place: Caesar with any shift you choose, ROT13, Vigenère with a keyword, and Atbash. Letters keep their case and everything else — digits, spaces, punctuation — passes through untouched, which is what makes the output readable and also what gives the game away: word lengths and shapes survive intact. ROT13 is simply Caesar with a shift of thirteen, which is why applying it twice returns the original. The brute-force panel shows all twenty-five non-trivial shifts at once, and it is the honest demonstration of why none of these is encryption — a Caesar message falls in seconds to a person scanning that list. Good for puzzles, escape rooms, CTF warmups and teaching how frequency analysis works.
Frequently asked questions
Are these secure?
No — they're educational and used in puzzles. Even Vigenère falls to frequency analysis once the key length is known. Use AES or modern ciphers for real security.
Why is ROT13 used at all?
Spoiler tags, joke punchlines, mild obfuscation. Because it's its own inverse, the same tool encodes and decodes.
What characters get shifted?
Only A-Z and a-z. Numbers, spaces, punctuation, and non-Latin scripts pass through untouched.
How is the brute-force panel useful?
When you know a message is Caesar-shifted but don't know the shift — scroll through all 26 outputs and pick the one that reads as plain text.
Why does the ciphertext still look like readable words?
Because only letters move — spaces and punctuation pass through untouched, so word lengths and shapes survive exactly. That is what makes these ciphers legible to work with and also what gives them away: a three-letter word at the start of an English sentence is almost certainly the.
Why does Vigenère resist the brute-force panel?
Because it uses a different shift per position, so there is no single shift to try. It falls to a different attack instead: find the key length by looking for repeated patterns, then treat every nth letter as its own Caesar cipher and solve each by letter frequency.
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