TheCipherBureau
TheCipherBureau is a playground for classical ciphers — Caesar, Vigenère, substitution, transposition, and friends. Type text, pick a cipher, watch it encrypt before your eyes; paste ciphertext, break it back open.
It exists because cryptology is one of those subjects that only clicks when you play with it. Reading about frequency analysis is boring. Watching a Vigenère ciphertext crack apart as the key length reveals itself is a magic trick you performed yourself.
The playground covers all three verbs:
- Encode — turn plaintext into ciphertext with any supported cipher.
- Decode — reverse it, with the key.
- Break — attack ciphertexts without the key: frequency counting, Kasiski examination, dictionary attacks.
Everything runs client-side in vanilla JavaScript — no server, no build step, just the page. The code for each cipher is small enough to read in one sitting, which is exactly the point: the site teaches, and so does its source.