Ciphers
Variant Beaufort cipher
A repeating-Key cipher using plaintext minus Key.
Also found as Variant · Beaufort variant · German variant
How it works
Variant Beaufort subtracts Key from plaintext. Decryption adds it back. It matches Vigenère with the shifts reversed, but the same written keyword produces a different result.ACA VariantMilitary Cryptanalysis, Part II
Cᵢ = (Pᵢ − Kᵢ) mod 26Pᵢ = (Cᵢ + Kᵢ) mod 26Worked example
- Keyword
APPLE- Plaintext
CEQUALSPMINUSK- Ciphertext
CPBJWLDABENFDZ
Recognition and naming
The ACA usually calls this cipher simply Variant. Decipher says Variant Beaufort to show the relationship. Periodic clues may identify the family. To tell its members apart, test a plaintext or Key guess under each formula.ACA Variant