Rotor machine: Encyclopedia II - Rotor machine - History

Rotor machine - History

Rotor machine - Invention

The concept of a rotor machine occurred to a number of inventors independently at a similar time.

In 2003, it emerged that the first inventors were two Dutch naval officers, Theo A. van Hengel (1875 – 1939) and R. P. C. Spengler (1875 – 1955) in 1915 (De Leeuw, 2003). Previously, the invention had been ascribed to four inventors working independently and at much the same time: Edward Hebern, Arvid Damm, Hugo Koch and Arthur Scherbius.

In the United States Edward Hugh Hebern built a rotor machine using a single rotor in 1917. He became convinced he would get rich selling such a system to the military, the Hebern Rotor Machine, and produced a series of different machines with one to five rotors. His success was limited, however, and he went bankrupt in the 1920s. He sold a small number of machines to the US Navy in 1931.

In Hebern's machines the rotors could be opened up and the wiring changed in a few minutes, so a single mass-produced system could be sold to a number of users who would then produce their own rotor keying. Decryption consisted of taking out the rotor(s) and turning them around to reverse the circuitry. Unknown to Hebern, William F. Friedman of the US Army's SIS promptly demonstrated a flaw in the system that allowed the ciphers from it, and from any machine with similar design features, to be cracked with enough work.

Another early rotor machine inventor was Dutchman Hugo Koch, who filed a patent on a rotor machine in 1919. At about the same time in Sweden, Arvid Gerhard Damm invented and patented another rotor design. However, the rotor machine was ultimately made famous by Arthur Scherbius, who filed a rotor machine patent in 1918. Scherbius later went on to design and market the Enigma machine.

Rotor machine - The Enigma machine

The most widely-known example of a rotor machine is the German Enigma machine used during World War II, of which there were a number of variants. The standard Enigma model, Enigma I, used three rotors. At the end of the stack of rotors was an additional rotor-like disk, wired such that the inputs were connected electrically back out to some other contact on the same side – in some sense, half of a normal rotor. When current was sent into most of these machines it would travel through the rotors and out the other side to the lamps, but in the Enigma it was "reflected" back through the disks before going to the lamps. The advantage to this system was that there was nothing that had to be done to the setup in order to decrypt a message, the machine was symmetrical at all times. The reflector guaranteed that no letter could be enciphered as itself, so an A could never turn back into an A, which helped British efforts to break the cipher. See Cryptanalysis of the Enigma.

Scherbius joined forces with a mechanical engineer named Ritter and formed Chiffriermaschinen AG in Berlin before demonstrating Enigma to the public in Bern in 1923, and then in 1924 at the World Postal Congress in Stockholm. In 1927 Scherbius bought Koch's patents, and in 1928 they added a plugboard, essentially a non-rotating manually-rewireable fourth rotor, on the front of the machine. After the death of Scherbius in 1929, Willi Korn was in charge of further technical development of Enigma.

As with other early rotor machine efforts, Scherbius had limited commercial success. However, the German armed forces, responding in part to revelations that their codes had been broken during World War I, adopted the Enigma to secure their communications. The German Navy adopted Enigma in 1926, and the German Army began to use a different variant around 1928.

The Enigma (in several flavors) was the rotor machine Scherbius' company, and its successor, Heimsoth & Reinke, supplied to the German military and to such assorted civilian agencies as the Nazi party security organization, the SD. The German Army version was the Enigma the Poles broke in the early 1930s not long after it was first used. They passed their progress on to the French and British in July 1939, and the British and French continued to break German Army Enigma — along with Luftwaffe Enigma traffic — until French cryptanalysis (at Station PC Bruno) was shut down. The British continued breaking Enigma and, assisted eventually by the United States, extended the work to German Naval Enigma traffic, most especially to and from U-boats during the Battle of the Atlantic.

Rotor machine - Various machines

During World War II (WWII), both the Germans and Allies developed additional rotor machines. The Allies developed the Typex (British) and the SIGABA (American). During the War the Swiss began development on an Enigma improvement which became the NEMA machine which was put into service after WWII. There was even a Japanese developed variant of the Enigma in which the rotors sat horizontally; it was apparently never put into service. The Japanese PURPLE machine was not a rotor machine, being built around electrical stepping switches, but was conceptually similar.

Rotor machines continued to be used even in the computer age. The KL-7 (ADONIS), an encryption machine with 8 rotors, was widely used by the U.S. and its allies from the 1950s until the 1980s. The last Canadian message encrypted with a KL-7 was sent on June 30, 1983.

A unique rotor machine was constructed in 2002 by Netherlands-based Tatjana van Vark [1]. This unusual device is inspired by Enigma, but makes use of 40-point rotors, allowing letters, numbers and some punctuation; each rotor contains 509 parts [2].

A software implementation of a rotor machine was used in the crypt command that was part of early UNIX operating systems. It was among the first software programs to run afoul of U.S. export regulations which classified cryptographic implementations as munitions.

Adapted from the Wikipedia article "History", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki