Enigma-G

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The Enigma-G was easy to transport due to its compact dimensions

The Enigma-G (also written: Enigma G or ENIGMA G and referred to as: defense Enigma , incandescent Enigma cipher machine with counter , briefly Zählwerksmaschine or counter-Enigma ) is a rotor cipher machine , which in the Second World War, particularly in the communications of the German Abwehr (secret service) was used for secret communication. By number of transfer notches ( see below ), it was by the British as 11-15-17-machine (ger .: 11-15-17 machine) designated.

construction

The counter can be seen up well left here in Figure 1 (drawing from. Patent US1657411 : Ciphering Machine. Me on Feb. 6, 1923 , inventor: Arthur Scherbius . )
Set of rollers and counter, including display and keyboard

The principle and basic structure of the Enigma is described in the overview article of the same name . In contrast to the Enigma I model, which is the focus of the explanations there, the Enigma-G is characterized by some special features. In addition to their particularly careful and compact design with the external dimensions (L × W × H) 270 mm × 250 mm × 165 mm, this also includes a number of special cryptographic features.

The Enigma-G uses an exclusive set of rollers (see also: Enigma rollers ) in which the three different rollers have not just a single transfer notch (like rollers I to V of the Enigma I) or two notches (like rollers VI to VIII of the Enigma M4 ) but have a large number of transfer notches. This means that the middle and left rollers are indexed much more frequently than with the other Enigma models. Furthermore, even the reverse roller (VHF) takes part in the rotation. This increases the combinatorial complexity of the machine and strengthens the cryptographic security. The Enigma-G is (apart from the little-used Enigma-Z ) the only Enigma model in which the VHF continues to rotate during the encryption (see also: Enigma models ).

Another special feature of the Enigma-G is the lack of a plug board . While this simplified the construction and handling of the machine and made it easier to use for defense agents , this measure weakened the encryption.

A non-cryptographic peculiarity of the Enigma-G is its gear, which is used to advance the rollers, as well as a special counter, similar to a mechanical odometer , which counts the number of keystrokes and thus the length of the entered and encrypted text. This enables good control of the input and - unlike all other models - the correction of typing errors, since the machine can be set back by a defined number of characters with the aid of the gearbox, which also enables the rollers to rotate backwards, and the counter can.

In contrast to the Enigma I, which was built in large numbers of tens of thousands of copies, only about a hundred Enigma counters were made.

Rollers

Soldiers of the secret radio reporting service of the OKW Foreign Office / Defense using the Enigma to encrypt or decrypt messages

As with all Enigma models, the heart of the machine is the set of rollers. With the Enigma-G it consists of three reels, which are marked with Roman numerals (I, II and III) and rotate during the encryption. At 85 mm, the diameter of the rollers is slightly smaller than that of the other models (100 mm). Due to this, the construction of the rollers also differs somewhat from the other models. The contact pins on the right-hand side are arranged on two concentric circles in a zigzag pattern and the contact surfaces on the left-hand side of the rollers are accordingly not circular, but teardrop-shaped. The rollers can be arranged ( permuted ) in any order by the user . With three rollers, this results in 3 · 2 · 1, that is to say six possible roller positions . There is also the FM, which cannot be selected, but also rotates.

The initial position of the VHF and the three rollers can be freely set by the user. There are 26 options for this, corresponding to the 26 capital letters of the Latin alphabet . This gives a total of 26 4 , i.e. 456,976 possible starting positions from AAAA to ZZZZ.

In order to achieve the most "irregular" possible rotation of the rollers, the number of transfer notches was drastically increased compared to the rollers of the Enigma models used by the Wehrmacht . Care was taken not to unnecessarily reduce the period length of 26 4 , i.e. 456,976, and the number of transfer notches of the three rollers to be coprime to one another and selected to be 26, namely 17, 15 and 11 notches for rollers I, II and respectively III.

The wiring of the rollers differed from those of all other models and was also not uniform within the model family. Presumably the wiring of the roller set was changed occasionally on some machines even during their lifetime. This served to better shield the various key groups and agents from one another and to increase the security of communication. For the details of the roller wiring and the transfer notches, see also: Enigma rollers .

Decipherment

The mansion (Engl. The mansion ) of Bletchley Park was the headquarters of the British code breaker and is now a museum

As with all other Enigma models succeeded the British code breakers to Alan Turing and Gordon Welchman in English Bletchley Park and in the Enigma G, the deciphering . The main reason for the success of the break-in was the omission of the plug board and the associated drastic reduction in the combinatorial complexity of the machine.

The British cryptanalyst Peter Twinn , one of Turing's employees in Bletchley Park, commented on this German mistake with the words "they certainly missed a trick in not combining multiple-turnover wheels with plug connections" (German: "They [the Germans] certainly missed a trick." by not combining rollers with several transfer notches and the plug connections ”).

The result was that on December 8, 1941, the British succeeded for the first time in deciphering a German radio message encrypted with the Enigma-G. Dillwyn "Dilly" Knox and his colleagues Mavis Lever and Margaret Rock played a key role in this success . As a result, this meant that German agents could be “received” as soon as they entered the United Kingdom. They were then not simply eliminated, but the British domestic secret service MI5 succeeded in "turning around" many of them and using them as double agents within the framework of the Double Cross system. Together with the information deciphered from Enigma-G sayings, the MI5 received such a detailed and accurate picture of the plans and the level of knowledge of the defense that every single German agent still operating in Great Britain was precisely known and could be specifically controlled and manipulated. This was also used to disinformation the German leadership (see also: Operation Fortitude ).

American cryptanalysts in the United States Coast Guard Unit 387 also succeeded in breaking the Enigma-G.

literature

  • Friedrich L. Bauer : Deciphered Secrets. Methods and maxims of cryptology. 3rd, revised and expanded edition. Springer, Berlin et al. 2000, ISBN 3-540-67931-6 .
  • Frank Carter: The Defense Enigma Machine . Publication, Bletchley Park. Accessed: January 4, 2011. PDF; 0.1 MB
  • David H. Hamer: G-312. To defense Enigma . Cryptologia. Rose-Hulman Institute of Technology. Taylor & Francis, Philadelphia PA 24.2000.1 (January), pp. 41 ff. ISSN  0161-1194 . Accessed: January 4, 2011. PDF; 1.1 MB
  • Michael Pröse: Encryption machines and deciphering devices in World War II - history of technology and aspects of IT history . Dissertation at Chemnitz University of Technology, Leipzig 2004. Accessed: January 4, 2011. PDF; 7.9 MB
  • Paul Reuvers and Marc Simons: Enigma G-111 . Crypto Museum , Eindhoven 2009. Accessed January 4, 2011. PDF; 9.8 MB
  • Peter Twinn: The Abwehr Enigma in Francis Harry Hinsley, Alan Stripp (Ed.): Codebreakers - The inside story of Bletchley Park . Oxford University Press, Reading, Berkshire 1993, pp. 123-131. ISBN 0-19-280132-5
  • Heinz Ulbricht: The Enigma cipher machine - deceptive security . A contribution to the history of the intelligence services. Dissertation Braunschweig 2005. Accessed: January 4, 2011. PDF; 4.7 MB

Web links

Individual evidence

  1. ^ David H. Hamer: G-312. To defense Enigma . Cryptologia. Rose-Hulman Institute of Technology. Taylor & Francis, Philadelphia PA 24.2000.1 (Jan), p. 42. ISSN  0161-1194 . Accessed: January 4, 2011. PDF; 1.1 MB
  2. ^ Army Security Agency: Notes on German High Level Cryptography and Cryptanalysis . European Axis Signal Intelligence in World War II, Vol 2, Washington (DC), 1946 (May), p. 9. Accessed: Feb. 28, 2011. PDF; 7.5 MB ( memento from June 11, 2014 in the Internet Archive )
  3. ^ David H. Hamer: G-312. To defense Enigma . Cryptologia. Rose-Hulman Institute of Technology. Taylor & Francis, Philadelphia PA 24.2000,1 (January), p. 46. ISSN  0161-1194 . Accessed: January 4, 2011. PDF; 1.1 MB
  4. ↑ Peter Twinn: The Abwehr Enigma in Francis Harry Hinsley, Alan Stripp: Codebreakers - The inside story of Bletchley Park . Oxford University Press, Reading, Berkshire 1993, p. 125. ISBN 0-19-280132-5
  5. ^ Frank Carter: The Defense Enigma Machine . Publication, Bletchley Park. Accessed: January 4, 2011. PDF; 0.1 MB
  6. ^ Hugh Sebag-Montefiore: Enigma - The battle for the code . Cassell Military Paperbacks, London 2004, p. 129. ISBN 0-304-36662-5
  7. ↑ Michael Smith: Enigma decrypted - The "Codebreakers" from Bletchley Park . Heyne, 2000, pp. 190 ff. ISBN 3-453-17285-X
  8. ↑ History Of Coast Guard Unit 387 , accessed December 28, 2018.