buttcrack. Cipher Wiki

Beaufort

From the Buttcrack Cipher Wiki — the free field guide to classical ciphers

Beaufort — C = K - P rather than P + K, which makes the cipher its own inverse: encrypting a ciphertext with the same key returns the plaintext.

C = K - P. Reciprocal: encryption and decryption are the same operation.

A worked example§

Encrypting a sample with the cipher itself, at build time:

MEET ME BY THE OLD CLOCK TOWER AT DAWN

Key: LEMON

produces the ciphertext

ZAIV BH DO VGH QBL LAQKE UXIIX NS BMSA

This example is generated by running the cipher when the page is built, and the round trip is checked, so it always matches what the solver does.

How it is broken§

Identical to Vigenere — period, then columns — with the sign of the column solve flipped.

History and context§

Named for Sir Francis Beaufort, the admiral behind the wind scale, and sold as a slide rule for the Royal Navy after his death.

See also§

Vigenère · Variant Beaufort · Gronsfeld · Porta · Quagmire III (keyed alphabet) · Sum-clock (additive wheels)

Browse every cipher in the Polyalphabetic ciphers family, read the history of codebreaking, or return to the wiki main page.

Frequently asked questions§

How is the Beaufort broken?

Identical to Vigenere — period, then columns — with the sign of the column solve flipped.

What key does the Beaufort use?

keyword. The keyspace is unbounded in practice.

How much ciphertext do I need?

At least 24 characters for this solver to attempt it; short messages can be readable and still not be proof.

Can I break a Beaufort on this page?

Yes — the browser solver on this page handles it directly. Paste the ciphertext into the solver and press the button.

Categories: Polyalphabetic ciphers | Breakable in the browser | Cipher wiki
The facts in this article are generated from buttcrack's cipher registry when the site is built, so they describe the implementation you can run on this page. Registry-generated content is checked against the code; the history is editorial.

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It tries: Caesar, Atbash, ROT13, affine, Trithemius, rail fence, single-byte XOR, periodic Vigenère-family ciphers, autokey, selected encoding layers (such as Base64, hex, binary, decimal ASCII, Morse, and reverse), and—only with 60+ A–Z letters—statistical substitution.

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