⌘ K
beaufort · self-inverse · keyword · live

Encode with the Beaufort cipher

Vigenere variant where the key letter is subtracted from instead of added to the plaintext. Encoding and decoding are the same operation. Runs locally.

Beaufort Cipher
Input
28 B
1 lines
Output
28 B
1 lines
Status
ready
live
Ratio
1.00×
out/in
input · text
output · beaufort
CKMPVCPVWPIWUJOGIUAPVWRIWUUK
Quick Start

How to use Beaufort

The output letter is computed as (key - plaintext) mod 26. Because subtraction is symmetric here, applying Beaufort twice with the same key recovers the original — no separate decrypt step.

  1. 01

    Enter a key

    Any alphabetic string. Non-letters are stripped before use.

    Bytes flow through TextEncoder/TextDecoder for predictable UTF-8 semantics — emoji, surrogate pairs, and combining marks all encode losslessly.

    keyUTF-8TextEncoderlosslesslive
    key · raw bytesFORTIFI... · UTF-8
    FORTIFICATION
    loaded · UTF-8MIME · ready
  2. 02

    Type or paste text

    Letters are transformed; digits and punctuation are kept as-is.

    Hash and signature operations call crypto.subtle from the Web Crypto API, so output matches OpenSSL / Node bit-for-bit.

    inputWeb Cryptosubtledeterministiclive
    input · optionstext · live
    DEFENDTHEEAST
    options applied · livelive
  3. 03

    Auto-symmetric

    out = (key - in) mod 26 — running Beaufort on its output returns the input.

    Options re-run instantly through useEffect + useMemo — switching URL-safe mode or padding doesn’t re-encode from scratch.

    self-inversememoisedoptionsinstantreactive
    rule · encodedk-p mod 26 · ready
    run twice → original
    encoded · livelossless
  4. 04

    Copy or download

    One click to clipboard. Download as .txt.

    Copy uses the Async Clipboard API; downloads ship via Blob with the appropriate MIME (text/plain, image/png, …) so external tools recognise them.

    exportclipboardblobMIME-correctclient-side
    ok · copiedready · done
    Copied
    shipped · ready to shipsuccess
Pro tips

Encoding without surprises

Always UTF-8 first

Use TextEncoder / TextDecoder for bytes ↔ string conversion. btoa alone breaks on non-ASCII.

URL-safe vs standard Base64

Standard uses +, /, =; URL-safe swaps to -, _, no padding. Don’t mix them.

Hashes aren’t passwords

SHA-256 is fast; that’s good for fingerprints, bad for passwords. Use bcrypt / argon2 for credentials.

Watch padding rules

Some decoders are strict about = padding, others auto-pad. If round-trips fail at exactly 1 or 2 bytes, check padding.

Use Web Crypto for keys

Generate cryptographic keys via crypto.subtle, never Math.random. The latter is predictable.

JWT decode ≠ verify

Decoding a JWT just splits and base64-decodes. Verification needs the issuer’s public key / shared secret.

Related toolsVigenere CipherCaesar CipherAffine CipherAtbash CipherSubstitution CipherRail Fence Cipher
Use Cases

When to use Beaufort

Naval-history reproductions, CTFs, classroom comparisons.

Crypto history

Used historically by the Royal Navy in field cipher devices. Output round-trips losslessly with the matching decoder — both run client-side, so end-to-end testing happens in a single tab. Encoding flows through TextEncoder for predictable UTF-8 semantics.

RFC-compliant

CTF puzzles

Variant of Vigenere — frequent in mid-level challenges. Web Crypto's subtle.digest produces output that matches OpenSSL, GPG, and Node's crypto module byte-for-byte. That makes the result trustworthy as a content fingerprint, ETag, or integrity check.

OpenSSL-matched

Teaching

Concrete example of a reciprocal polyalphabetic cipher. Pairs cleanly with HMAC, JWT, and signed-URL workflows where bit-level correctness matters. The browser's crypto stack is FIPS 140-validated in Chrome and Firefox, so it's production-grade.

lossless

Tableau study

Compare to the Vigenere square to highlight the difference. Output uses canonical RFC 4648 / 7515 alphabets so curl, openssl, and any standards-compliant decoder accept it as input. URL-safe variants drop padding for tokens that travel in query strings.

byte-identical

Reproduction

Recreate ciphertexts from period archives. Heavy hashing runs through useMemo so large inputs don't block typing. PBKDF2, bcrypt, and Argon2 expose configurable cost factors — tune for your threat model, not the default.

spec-grade

Cross-tool checks

Sanity-check Beaufort implementations across languages. Same input plus same options always yields identical bytes. That's the foundation for content-addressed storage (IPFS, Git, S3 ETags) and means the output is safe to commit to fixtures.

production-ready
FAQ

Frequently asked questions

Vigenere adds the key letter to the plaintext; Beaufort subtracts the plaintext from the key. The subtraction makes Beaufort self-inverse.
Encoding and decoding are the same operation. Apply the tool a second time with the same key and the original text comes back.
Output preserves input case. The key is normalised to uppercase letters only.
No — same weaknesses as Vigenere. Repeated short keys are broken by Kasiski/IC analysis.
No. The cipher runs locally in your browser.
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