The ''Schlüsselgerät'' 41 ("Cipher Machine 41"), also known as the SG-41 or Hitler mill, was a

rotor cipher machine In cryptography, a rotor machine is an electro-mechanical stream cipher device used for encrypting and decrypting messages. Rotor machines were the cryptographic state-of-the-art for much of the 20th century; they were in widespread use in the 19 ...

, first produced in 1941 in Nazi Germany, that was designed as a potential successor for the Enigma machine. It saw limited use by the ''

Abwehr The ''Abwehr'' (German for ''resistance'' or ''defence'', but the word usually means ''counterintelligence'' in a military context; ) was the German military-intelligence service for the ''Reichswehr'' and the ''Wehrmacht'' from 1920 to 1944. A ...

'' (military intelligence) towards the end of World War II.

History

The SG-41 was created under order of the '' Heereswaffenamt'' ( Inspectorate 7/VI organisation) as a collaboration between German cryptographer

Fritz Menzer Ostwin Fritz Menzer (6 April 1908 in Herrndorf near Niederschöna in Saxony between Chemnitz and Dresden – 25 October 2005 in Bad Homburg vor der Höhe) was a German cryptologist, who before and during World War II, worked in the In 7/VI, the ...

and Wanderer, a leading typewriter manufacturer. The machine also acquired the nickname "Hitler mill" because of the large crank attached to the side of the unit. Instead of using a lampboard like the Enigma, the SG-41 printed both the plaintext and ciphertext of the message onto two paper tapes. Due to wartime shortages of light metals such as aluminium and magnesium, the SG-41 weighed approximately , which made it unsuitable for the front lines. Menzer intended for the SG-41 to fully replace Enigma, which he considered to no longer be secure; the '' Luftwaffe'' and ''

Heer Heer may refer to: People * Jeet Heer, Canadian author and journalist * Jeffrey Heer (born 1979), American computer scientist and entrepreneur * Kamal Heer (born 1973), Punjabi singer and musician * Oswald Heer (1809–1883), Swiss botanist and ...

'' ordered around 11,000 units. A total of 1,000 units were produced. Various sources have reported production figures as low as 500 units due to materiel shortages, but production was halted after 1,000 units, as it was considered too heavy for use on the front. In December 1943, General Fritz Thiele ordered production to cease by the end of 1944. Beginning on 12 October 1944, the first deliveries to the ''

'' began. In the final months of the war, the SG-41 was used instead of the ''Abwehr'' Enigma.

Function

Functionally, the machine had greater similarities with the

Boris Hagelin Boris Caesar Wilhelm Hagelin (2 July 1892 – 7 September 1983) was a Swedish businessman and inventor of encryption machines. Biography Born of Swedish parents in Adshikent, Russian Empire, Hagelin attended Lundsberg boarding school and late ...

C-Series. The SG-41 had six encryption rotors, compared to the Enigma, which had either three or four, in addition to a number of advanced features, making it much more resistant to cryptanalysis than the Enigma or other contemporary Hagelin machines. While the Enigma rotors advanced by one for each letter enciphered, the SG-41's wheels interacted with each other and moved irregularly. Similar functionality was not adopted in a mass-produced cipher machine until 1952 with the advent of the Hagelin

CX-52 The (Hagelin) C-52 and CX-52 were cipher machines manufactured by Crypto AG starting 1951/1952. These pin-and-lug type cipher machines were advanced successors of the C-38/M-209. The machine measures . The device is mechanical, but when combi ...

Cryptanalysis

The Allied codebreakers in Bletchley Park considered the device a "mystery". Only a handful of messages were able to be deciphered during the war, namely when two messages were " in depth" i.e. encrypted with the same key. The inner workings of the device were unclear until after the war, so it was not possible to perform a systematic cryptanalysis on the messages. Allied codebreakers referred to it as a "remarkable machine".

SG-41Z

In the final months of the war, an additional 550 units were built, which are referred to as the SG-41Z. This model only allowed the numbers 0–9 to be enciphered and was used by the '' Luftwaffe'' for weather reports.

Find near Aying

On 5 May 2017, two hobbyist treasure hunters found an SG-41 using a metal detector in a forest near the Bavarian city of

Aying Aying is a municipality in the district of Munich in Bavaria, Germany. It is known for the Ayinger Brewery Ayinger Brewery ( ; german: Brauerei Aying) is in Aying, Bavaria, Germany, about 25 km south of Munich. Ayinger beers are exported ...

, buried approximately deep. The hobbyists donated their find to the Deutsches Museum in Munich instead of selling it privately. The museum intends to conserve it in its current condition and display it in a new permanent exhibit, ''BildSchriftCodes''.

References