Rangdom

Encode text with a keyword

The Beaufort cipher repeats your keyword across the message and replaces each letter with (key − plaintext) mod 26. It uses the same keyword mechanic as Vigenère but a different formula, which is why the two are often confused.

When to use this tool

Reach for the Beaufort cipher when a puzzle or CTF challenge uses a repeating keyword but the usual Vigenère decode does not produce readable text — the two share the same keyword mechanic but apply a different formula, so they are easy to confuse. Beaufort replaces each letter with (key − plaintext) mod 26 and is self-reciprocal, meaning the same operation both encodes and decodes. Pick a keyword, then encode or decode on a single page.

Privacy and limitations

Everything runs locally in your browser; nothing is sent anywhere. This is a classical polyalphabetic cipher, not real encryption — it only transforms A–Z and a–z, leaves digits and symbols untouched, and offers no autokey, variant (German) Beaufort, or auto-solving features. Because the transform is its own inverse, encode and decode produce identical results; you still need the exact keyword to recover a message.

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