Duenna

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Duenna was an electromechanically operated cryptanalytic machine that was developed and used by the US towards the end of the Second World War to decipher the communications of the German Wehrmacht, which was encrypted using the ENIGMA key machine . The British code breaker Conel Hugh O'Donel Alexander described in a (then) secret report in 1944, the year of the war, a procedure that could be carried out manually, called hand duenna .

The origin of the name is not finally clear. The name "Duenna" was possibly inspired by the cryptanalytic attack method used here, called " two-wheel attack ". The first syllable "Du ~" could thus be derived from Latin dualis (German: containing two), while the second part of the name "~ enna" suggests the name ENIGMA. This explanation fits that the concept of a forerunner machine from Duenna , which only considered a single roller, was given the name Mona , which was probably derived from "monos" ( ancient Greek μόνος , German "alone" or "only"). The Mona machine was never realized.

background

ENIGMA roller set with three rotating rollers and on the far left here the reversing roller B. Duenna's task was to develop the unknown and frequently changing wiring of the reversing roller D.

During the Second World War, the backbone of German cryptography was formed by ENIGMA, which was used by all three parts of the Wehrmacht, the army , the air force and the navy , to encrypt their secret communications. Long before the war, in 1932, Polish cryptanalysts working with the young Marian Rejewski succeeded in breaking into the ENIGMA system for the first time . Building on this, British code breakers in Bletchley Park (BP), England, managed to intercept German radio messages at the beginning of the war and, from January 1940, first of all to decipher the messages encrypted by the Luftwaffe and later also by the army with the ENIGMA I. Contrary to the German hopes and assumptions, the radio messages encrypted by the German Navy with the help of the ENIGMA M3 and - particularly important for the war effort - the radio messages encrypted with the ENIGMA M4 machine used by the German submarines remained no secret for the British. Rather, they succeeded in breaking the Wehrmacht's encrypted communications with the aid of special cryptanalytic devices such as the Turing bomb for almost the entire duration of World War II and using the information obtained from it profitably under the code name " Ultra ".

Towards the end of the war, more precisely on January 1, 1944, the Luftwaffe began to use an innovative roller in part of its key networks, namely the reversing roller D (photo see Pröse p. 40), which, in contrast to all other ENIGMA rollers, is characterized by this that their wiring could be changed by the user depending on the key . The German cryptographers thus eliminated a major weakness of ENIGMA, which was based on the fact that, as with the "old" reversing rollers (VHF A, B and C), the wiring of the ENIGMA rollers was rigid and never changed (see also: ENIGMA rollers ). So they denied their British and American "opponents" the possibility of breaking into the secret German radio traffic, which was used there on an industrial scale, but without the Germans knowing or even suspecting it.

The VHF D could have had fatal consequences due to the significant increase in the combinatorial complexity of the ENIGMA machine on the Allied side, and could have caused the ENIGMA to completely lose its ability to decipher if this cylinder had been introduced suddenly and across the board. This is confirmed by a quote from an American investigation report written shortly after the war:

“ How close the Anglo-Americans came to losing out in their solution of the German Army Enigma is a matter to give cryptanalysts pause. British and American cryptanalysts recall with a shudder how drastic an increase in difficulty resulted from the introduction by the German Air Force ot the pluggable reflector ("Umkehrwalze D," called "Uncle Dick" by the British) in the Spring of 1945. It made Completely obsolete the "bomb" machinery which had been designed and installed at so great an expense for standard, plugboard-Enigma solution. It necessitated the development by the US Navy of a new, more complex machine called the "duenna," and by the US Army of a radically new electrical solver called the "autoscritcher." Each of these had to make millions of tests to establish simultaneously the unknown (end-plate) plugboard and the unknown reflector plugging. Only a trickle of solutions would have resulted if the pluggable reflector had been adopted universally; and this trickle of solutions would not have contained enough intelligence to furnish the data for cribs needed in subsequent solutions. Thus even the trickle would have eventually vanished. ”

“How close the Anglo-Americans were about to lose the ability to decipher the German Army ENIGMA is a matter that makes cryptanalysts breathless. British and American code breakers remember with a shudder what a drastically increased complication from the introduction of the plug-in reversing roller ("Reversing roller D", called "Uncle Dick" by the British) by the German Air Force in the spring of 1945 [actually: in the spring of 1944] resulted. This made the " bomb fleet " completely useless, which had been designed and built with so much effort to solve the normal plug board ENIGMA. Inevitably, the US Navy had to develop a new, much more complicated machine called the “Duenna”, and the US Army had to develop a completely new electrical solution machine called the “ Autoscritcher ”. Each of these machines had to carry out millions of tests in order to simultaneously fathom the unknown (front panel) connector board and the unknown wiring of the reversing roller [D]. There would only have been a trickle of solutions if the plug-in reversing roller had been used in general; and these droplets of solution would not have contained sufficient information to provide indications for cribs needed for further solutions. In the end, even the trickling would have dried up. "

In fact, the reversing roller D was not introduced suddenly and across the board, but, presumably due to production bottlenecks caused by the war and also, as has since been done by the German cryptologist Dr. Erich Hüttenhain known, because of its arduous and error-prone handling only occasionally and in a few key circles, for example by the Air Force in Norway, while mostly the well-known VHF B was still used - a fatal cryptographic error.

This mistake allowed the Allies to understand the functionality and use of the VHF D and to develop special cryptanalytic "cracking machines", the main task of which was to change the wiring of the VHF three to four times a month at intervals of about seven to twelve days D to stay on the trail and thus maintain the ability to decipher German communications, which is essential for the war effort.

Hand duenna

The British cryptanalyst CHO'D. In the war year 1944, i.e. the year at the beginning of which the German Air Force introduced the VHF D, Alexander described in an internal document a manual procedure with the help of which the unknown and frequently changing wiring of the VHF D should be made accessible. The British made this document available to their American allies and Alexander, who stayed with his colleagues in Washington for about six weeks in February and March 1944, refined the method on the ground. The procedure required knowledge of a crib (i.e. a suitable ciphertext / plain text fragment), the length of which had to be significantly greater than with the methods commonly used in BP using the Turing bomb . While about 20 to 25 letters were sufficient for these cribs , cribs of about 80 to 100 letters were required for the success of Hand Duenna .

The basic cryptanalytical principle of the process is based on the so-called " two-wheel attack ". The Allied cryptanalysts exploited a fundamental weakness of ENIGMA, which consisted in the fact that the roller position of the left roller in the roller set only changed every 650 letters, which, due to the prescribed maximum length of the radio messages of 250 letters, rarely happened once in a single message. It was therefore sufficient to just “play through” the 5 · 4 = 20 possible combinations of the middle and right-hand rollers and you did not have to examine all 60 combinations of the roller set. In addition, they used the “ general plug approach ” method and were thus able to further reduce the number of roller positions to be checked for two rollers from 26 · 26 = 676 possibilities to only 26 possible relative positions.

Overall, the search space shrank enormously and instead of the originally considered 60 roller positions times 17,576 roller positions, i.e. 1,054,560 (more than a million) possibilities of ENIGMA, the code breakers were able to make their work much easier and with only 20 26 = 520 investigating cases. A separate form was printed for each of these 520 cases, thus simplifying the evaluation.

Hand Duenna , as a manual procedure, was intended to help bridge the time during which the Allies did not yet have a mechanical procedure for determining the wiring of the VHF D, and thus preserve the continuity, which is crucial for the continued preservation of the deciphering ability of the ENIGMA . The Allies feared a drastic expansion of the use of the VHF D also in key areas of the Navy on August 1, 1944, after it was initially only used by the Germans in a few key areas of the Luftwaffe. In fact, their fears did not come true and they were relieved to find that the VHF D continued to be used only rarely and mostly the well-known VHF B (with rigid wiring) was used.

Duenna

The machine version of the method described was started on February 25, 1944 in the National Cash Register Company (NCR) in Dayton , Ohio in the USA under the direction of OP-20-G , a secret service group of the US specializing in cryptanalysis and signals intelligence . Navy , developed. The concept of the machine comprised a distribution switch driven by an electric motor, which rotated synchronously with the “fast” roller (the roller on the far right in the ENIGMA roller set). In this way, the plain / ciphertext letter pairs given by the crib were processed one after the other , which the code breakers referred to in technical jargon as "Constatations" . With the help of mechanical switches, the operator could also set the assumed or assumed connector partners of the individual letters. In contrast to the practically unmanageable task of trying out all the options for the entire ENIGMA plug board (there are more than 150 billion plug-in options for this, see also: Key space in the ENIGMA main article ), the plug partners can be tried out very easily for a single given letter, because there are only 26 possibilities for this.

The machine determined the resulting wiring of the VHF for each pair of letters of the crib under the respectively assumed boundary conditions. Then the results were compared with each other contradictions (English: Contradictions ) or confirmations (English: Confirmations ) could be found. In the first case, based on the basic principle of “ Reductio ad absurdum ” (German: return to contradiction), this case could be safely rejected as a possible solution. In the other case, a so-called “stop” had been found, ie a point that might represent the solution. In most cases, this was not the case, which had to be verified or falsified on the basis of subsequent investigations.

BP rated the mechanized duenna as the most effective method of attack against the VHF D. In fact, the Allied cryptanalysts achieved the greatest success with this machine. After the first prototype was finally used on November 16, 1944 after several months of starting difficulties, the first “break” occurred on December 26th. By the end of the war, thirteen more successes were added, which in total means more than half of all allied solutions by German UKW D. Duenna thus represents the most successful allied "cracking machine" against the German VHF D.

glossary

  • Confirmation - English word for "confirmation"
  • Constatation - Special English term for a pair of letters made up of a ciphertext letter at a certain text position and the associated assumed or assumed plaintext letter
  • Contradiction - English word for "contradiction"
  • Crib - (German: Eselsbrücke, more aptly: Probable word) English term for a text fragment which is expected to appear in plain text
  • Ciphertext - Text generated from plaintext by encryption
  • Key - Secret setting of the key machine
  • Key space - set of all possible keys
  • Spruch - ciphertext that is usually transmitted by radio
  • Plug - cable connections between the front panel sockets
  • Plug board - socket plate attached to the front of the ENIGMA
  • Reversing roller - (mostly) fixed roller at the end of the roller set (abbreviation: UKW)
  • Uncle Dick - (German: Onkel Dick) English nickname for the reversing roller D
  • Roller - rotor that turns during the keying process (English: wheel )
  • Roll position - key-dependent placement of the rolls in the roll set
  • Roller set - a summary term for all rollers
  • Roller position - manually adjustable and changing rotation position of the rollers during the keying process

See also

literature

  • CHO'D. Alexander : Hand Duenna . Publication, Bletchley Park 1998, PDF; 0.1 MB.Retrieved October 24, 2016.
  • Friedrich L. Bauer : Deciphered Secrets. Methods and maxims of cryptology. 3rd, revised and expanded edition. Springer, Berlin a. a. 2000, ISBN 3-540-67931-6 .
  • Philip Marks : Reversing roller D: Enigma's rewirable reflector - Part 1 . Cryptologia , Volume XXV, Number 2, April 2001, pp. 101-141.
  • Philip Marks: Reversing roller D: Enigma's rewirable reflector - Part 2 . Cryptologia, Volume XXV, Number 3, July 2001, pp. 177-212.
  • Philip Marks: Reversing roller D: Enigma's rewirable reflector - Part 3 . Cryptologia, Volume XXV, Number 4, Oct. 2001, pp. 296-310.
  • 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. PDF; 7.9 MB
  • Tony Sale: The Bletchley Park 1944 Cryptographic Dictionary . Publication, Bletchley Park, 2001, p. 22. Accessed: Jan. 24, 2012. PDF; 0.4 MB
  • Heinz Ulbricht: The Enigma cipher machine - deceptive security . A contribution to the history of the intelligence services. Dissertation Braunschweig 2005. PDF; 4.7 MB

Web links

Individual evidence

  1. ↑ a b C.H.O'D. Alexander: Hand Duenna. (PDF; 0.1 MB) In: Publication, Bletchley Park 1998. Archived from the original on May 30, 2005 ; accessed on January 24, 2012 (English).
  2. ↑ a b Philip Marks: Umkehrwalze D: Enigma's rewirable reflector - Part 2 . Cryptologia, Volume XXV, Number 3, July 2001, p. 192
  3. ↑ Philip Marks: Umkehrwalze D: Enigma's rewirable reflector - Part 2 . Cryptologia, Volume XXV, Number 3, July 2001, p. 193
  4. ^ Gordon Welchman: The Hut Six Story - Breaking the Enigma Codes . Allen Lane, London 1982; Cleobury Mortimer M&M, Baldwin Shropshire 2000, p. 11. ISBN 0-947712-34-8
  5. ^ Gordon Welchman: The Hut Six Story - Breaking the Enigma Codes . Allen Lane, London 1982; Cleobury Mortimer M&M, Baldwin Shropshire 2000, p. 230. ISBN 0-947712-34-8
  6. ↑ Michael Pröse: Encryption machines and deciphering devices in the Second World War - the history of technology and aspects of the history of IT . Dissertation at Chemnitz University of Technology, Leipzig 2004, p. 40. PDF; 7.9 MB ( Memento of the original from September 4, 2009 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / archiv.tu-chemnitz.de
  7. ↑ Philip Marks : Umkehrwalze D: Enigma's rewirable reflector - Part 1 . Cryptologia , Volume XXV, Number 2, April 2001, p. 107
  8. ^ A b 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. 13. Accessed: Jan. 24, 2012. PDF; 7.5 MB ( memento from June 11, 2014 in the Internet Archive )
  9. ↑ Friedrich L. Bauer: Deciphered secrets. Methods and maxims of cryptology. 3rd, revised and expanded edition. Springer, Berlin a. a. 2000, p. 118.
  10. ^ Hugh Sebag-Montefiore: ENIGMA - The battle for the code . Cassell Military Paperbacks, London 2004, p. 404 ISBN 0-304-36662-5
  11. ↑ Philip Marks: Umkehrwalze D: Enigma's rewirable reflector - Part 3 . Cryptologia, Volume XXV, Number 4, Oct. 2001, p. 296.
  12. ↑ Philip Marks: Umkehrwalze D: Enigma's rewirable reflector - Part 2 . Cryptologia, Volume XXV, Number 3, July 2001, p. 199
  13. ↑ Tony Sale: The Bletchley Park 1944 Cryptographic Dictionary . Publication, Bletchley Park, 2001, p. 22. Accessed: Jan. 24, 2012. PDF; 0.4 MB