Rotor Ciphermachines—as is generally believed—were invented independently by four different people around 1920:
(*) Damm's half rotors had only 5 contacts because they were destined for the 5-bit characters of a teleprinter. Later the Japanese constructed half rotors with 26 contacts.
Exercise. Analyze the change of the substitution of a half rotor when it rotates by one or by several positions.
Arvid Damm's company changed over to Boris Hagelin (1892–1983) in 1927, who relocated it to Zug in Switzerland in 1948 under the name Crypto AG. Hagelin seems to be the only man ever who made a fortune as Cryptologist.
In the last years the picture of the invention of rotor machines has significantly changed. (In 2014 there is even a rumor that in Norway there was rotor machine already in 1904. There is no published evidence up to now.)
Strong doubts arose that Koch was really an inventor. Virtually the same machine was built for the Dutch Navy already in 1915. The engineers were the officers Theo A. van Hengel (1875–1939) and R. P. C. Spengler (1875–1955). This invention—remember we are in the middle of World War I—was kept secret. In 1919 the Navy was no longer interested in the machine. Therefore van Hengel and Spengler asked for permission to file the patent. At the same time they handed the construction plan over to a patent agency. While van Hengel und Spengler waited for permission Koch filed an astoundingly similar patent. As it turned out much later Koch was the brother-in-law of the patent agent Huybrecht Verhagen. This could raise suspicion of plagiarism. However it seems more plausible that the officers got cold feet and feared a prosecution for high treason—the filing of the patent for a yet classified military device by officers. But the prosecution was pointless if the machine was already publicly known, say by a prior patent application. And to this end Koch might serve as a straw man. Another peculiarity: Koch never tried in any way to exploit his patent. He not even knocked together a single prototype!
Also the role of the Dutch Navy Ministry is obscure. Did they attempt to suppress evidence of a cooperation of the neutral Netherlands with German companies in the production of military equipment? An even more astounding observation is that the first version of the Enigma—Model A—was quite similar to the machine by van Hengel and Spengler. Unfortunately no exemplars of the Dutch machine survived, there only exists a somewhat sketchy description. But there is more evidence: Scherbius company (then »Gewerkschaft Securitas«, from 1923 on »Chiffriermaschinen AG«) was tightly affiliated with Koch's Dutch company (»Naamloze Vennootschap Ingenieursbureau Securitas«), he even completely took it over in 1928 including the patent. Was Scherbius also a plagiarist? To file his patent in 1918 he must have had informations already during the war! Even more evidence of high treason? Or a dubious cooperation via a dummy company? A historical thriller about dirty work, economic espionage, and high treason? Source:
Karl de Leeuw: The dutch invention of the rotor machine, 1915–1923. Cryptologia 27 (2003), 73–94.Unfortunately only the patent documents support this story, there are no other proofs. But there seems to be some evidence that the four person list of inventors should be replaced with van Hengel, Spengler, Hebern, and Damm.
(**) The letter stands for the series, the number (two digits) for the year. There could be a third digit for a variant.For the cryptanalysis of the M-209—and the American publication policy— see also
The series A and B used a plaintext alphabet of 25 letters. The letters were written into a 5-by-5 square, the two coordinates each were transformed by a half-rotor à la Damm.
Beginning with the C series the machines used no electro-mechanical rotors anymore but were purely mechanical machines with pin-wheels and a rotating drum with lug bars.
(***) The Americans, after the war, used the denotation »Menzer device«. This doesn't suit the historical facts: Menzer was only a clerical assistent at the Army's High Command who noted the requirements for the then new machine.
Two other German encryption machines played a major role in World War II. These were not rotor machines in the strong sense but electro-mechanical key generator machines:
The standard reference for rotor ciphermachines is Deavours/Kruh, see the Reference and Book List.
A comprehensive tutorial on breaking the (mechanical) Hagelin machine M-209 is
Wayne G. Barker: Cryptanalysis of the Hagelin Cryptograph. Aegean Park Press, Laguna Hills 1977.
A systematic description of Fialka is in
Eugen Antal and Pavol Zajac: Key space and period of Fialka M-125 cipher machine. Cryptologia 39 (2015), 126–144.