Beaufort cipher [SEP] named after
Beaufort cipher
The Beaufort cipher, created by Sir Francis Beaufort, is a substitution cipher similar to the Vigenère cipher, with a slightly modified enciphering mechanism and tableau. Its most famous application was in a rotor-based cipher machine, the Hagelin M-209. The Beaufort cipher is based on the Beaufort square which is essentially the same as a Vigenère square but in reverse order starting with the letter "Z" in the first row, where the first row and the last column serve the same purpose.
Using the cipher
, let formula_1 be the characters of the message, formula_2 be the characters of the cipher text and formula_3 be the characters of the key, repeated if necessary. Then Beaufort encryption formula_4 can be written,
Similarly, decryption formula_6 using the key formula_7,
Decrypting as a Vigenere cipher.
Due to the similarities between the Beaufort cipher and the Vigenère cipher it is possible, after applying a transformation, to solve it as a Vigenère cipher. By replacing every letter in the ciphertext and keytext with its opposite letter (