Key device 39

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The key device 39 (SG-39) was a rotor key machine that was developed in the 1930s in the German Reich by the company Telefonbau & Normalzeit (T&N). In 1939 a prototype was completed and submitted to the Army Weapons Office ; but not accepted due to the alleged lack of series production. The project was temporarily revived in 1943 and 1944, but it did not go into series production. The key device 39 was not used in World War II .

functionality

The functionality of the key device 39 was very similar to the Enigma-M4 . Like the Enigma-M4, it had three rotors that moved further in the course of the encryption or decryption, a fourth rotor (stator) that did not move automatically but could be set by hand and a non-movable reversing roller (VHF). In contrast to most of the Enigma variants (except those with the UKW D ), the UKW could be changed using a plug board. In contrast to the Enigma (which only had a single plug board ), the cipher device 39 had a second plug board which, like the Enigma, additionally permuted the letters entered via the keyboard before and after passing through the rotors. It is not clear whether this plug board, unlike the Enigma, was not involutive . The output of ciphertext and plain text took place via a printer and not via a lamp field as with the Enigma.

The main difference to the Enigma can be seen in the way in which the rotation of the rotors was enabled for encryption and decryption . There were three rotors (also known as rollers or wheels) with 21, 23 and 25 positions respectively. At each of these positions, a pen could be placed in either an active or inactive position. The wheels always moved one position further with the keying of a letter. The rotor assigned to a wheel then moved one position further when the pin was in the active position at the respective position of the wheel. In addition, each of the rotors was equipped with additional non-settable pins, which also influenced their progression.

At the instigation of the navy , it was determined at the end of 1942 that every new key machine that could be used by higher command posts had to be compatible with the Enigma . For this reason, the rotors of the cipher device 39 were equipped with movable rings, similar to the Enigma, to which the above-mentioned non-settable pins were attached to replace the transfer notches of the Enigma rotors. In order to additionally ensure interoperability with the Enigma-M4, the fourth rotor that does not advance further was finally added.

rating

The cipher device 39 avoided one of the main weaknesses of the Enigma via the irregular movement of the rotors . In addition, a possible non-involved plug board would have made the work of the Allied cryptanalysts even more difficult. In Michael Pröse's dissertation it is mentioned that other authors even hold the opinion that the Allies could not have deciphered the messages encrypted with this machine. The author of a report on the investigations carried out within the framework of TICOM also came to the conclusion in 1946 that the level of security of the encryption device 39, if used correctly, would probably correspond to that of SIGABA . On the other hand, it is assumed that because of the sheer necessity, methods of deciphering would have been developed.

literature

  • Michael Pröse: Encryption machines and deciphering devices in World War II - the history of technology and aspects of IT history , dissertation at Chemnitz University of Technology, Leipzig 2004. PDF; 7.9 MB

Web links

Individual evidence

  1. ↑ Michael Pröse: Encryption machines and deciphering devices in the Second World War - the history of technology and aspects of the history of computer science , dissertation at Chemnitz University of Technology, Leipzig 2004, p. 42ff. PDF; 7.9 MB ( Memento from September 4, 2009 in the Internet Archive )
  2. ↑ German cipher machines of World War II (English) ( Memento on 10 May 2009 at the Internet Archive ) (PDF, 1.1 MB), p 23
  3. ↑ Otto Buggisch: Final report written by Wachtmeister Otto Buggisch of OKH / CHI and OKW / CHI , TICOM I-137, October 1945, p. 2. TICOM I-137
  4. ↑ Otto Buggisch: Final report written by Wachtmeister Otto Buggisch of OKH / CHI and OKW / CHI , TICOM I-137, October 1945, p. 6. TICOM I-137
  5. ↑ Michael Pröse: Encryption machines and deciphering devices in World War II - the history of technology and aspects of the history of computer science , dissertation at Chemnitz University of Technology, Leipzig 2004, p. 43. PDF; 7.9 MB ( Memento from September 4, 2009 in the Internet Archive )
  6. ↑ European Axis Signal Intelligence in World War II - Volume 2: Notes on German High Level Cryptography and Cryptanalysis (English) ( Memento from June 11, 2014 in the Internet Archive ) (PDF; 7.5 MB), p. 17
  7. ↑ German cipher machines of World War II (English) ( Memento on 10 May 2009 at the Internet Archive ) (PDF, 1.1 MB), p 29