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 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. It belongs to the family of polyalphabetic substitution methods, and its close relationship to the Vigenère cipher is the main way it is described and taught.