Gjøvik University College Cryptology 1

2 Rotor cipher machines

In cryptography a rotor machine is a mechanical or electro-mechanical stream cipher machine. These machines first came into existence in 1915, with the two Dutch naval officers Theo A. van Hengel and R. P. C. Spengel invention. Little is known about this first machine, and other of the earliest machines, invented by men like Edward Hugh Hebern in 1917, Arvid Gerhard Damm in 1919 and Hugo Alexander Koch in 1919. In 1918 Arthur Scherbius filed a patent for his first rotor machine, and in the early 1920s he had invented the first rotor machine that got really famous, and still today is the most famous of them all, the Enigma. Used by the Axis nations, cryptanalyzed and cracked by among others Allan Turing at Bletchley Park during WW2. Its cryptanalyze work was groundbreaking in the world of computers. The Enigma have been the theme of multiple books and even a couple of movies.

A cryptographic rotor cipher machines implements a polyalphabetic substitution, with one or multiple rotors to make the cipher complex. The rotors are often key-wheels, where the initial cipher key is set, and the wheels turn in a regular or irregular way for each enciphered letter.

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The Hagelin M-209 cipher machine

How the key-wheels interact with the enciphering/deciphering process is most often determined by internal settings in the machine.