Beaufort cipher
Beaufort cipher, classical cipher, a puzzle not a protection, computed on your device.
Beaufort cipher computes C equals K minus P modulo 26 per letter, cycling key, letters only, across your text. The formula is its own inverse, so running it again with the same key recovers the plaintext, which is why there is no separate decode tool. Non-letters copy straight through without moving the key forward, and an empty key is refused.
Questions
How is Beaufort different from Vigenere?
The formula subtracts the plaintext from the key, C equals K minus P, rather than adding the key to the plaintext, which makes the operation its own inverse.
Is there a separate decode tool?
No, running the same tool a second time with the same key returns the original text, since the formula is involutory.
What happens to non-letter characters?
They pass through unchanged and do not advance the key position.
What if my key has no letters?
The tool refuses with "key must contain at least one letter".
Is this secure?
No, it is a classical cipher broken by the same frequency and Kasiski methods that break Vigenere; use AES-GCM encrypt for real protection.
Can I use this from the command line?
Yes, the same code runs on the page, the CLI and MCP.