Beaufort Cipher

About this calculator

This tool encrypts or decrypts text with the Beaufort cipher, a polyalphabetic cipher closely related to Vigenère but defined as ciphertext = key − plaintext (mod 26) instead of plaintext + key. This makes it reciprocal: running the exact same operation with the same key on the ciphertext recovers the plaintext, so encryption and decryption use one identical process.

Named after Sir Francis Beaufort (though invented by Giovanni Sestri), it saw real use in 19th-century cipher devices, including a variant in German naval Enigma procedures. Cryptography students and enthusiasts use this calculator to explore reciprocal ciphers and compare them to Vigenère. Enter your text and a keyword to encrypt or decrypt.