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The Beaufort cipher, invented by some Giovanni Sestri in early 18th century but widely attributed to Sir Francis Beaufort,[1] is a substitution cipher similar to the Vigenère cipher, with a slightly modified enciphering mechanism and tableau.[2] Its most famous application was in a rotor-based cipher machine, the Hagelin M-209.[3] 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,[4] where the first row and the last column serve the same purpose.[5]