Turing bomb

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A Wren operates the Turing bomb (recreated scene from Bletchley Park)

The Turing Bomb (also Turing-Welchman-Bomb or Welchman-Turing-Bomb ) is an electromechanical machine that was used by the British cryptanalysts in Bletchley Park (BP) during the Second World War to transmit the radio messages encrypted with the German key machine Enigma to decipher .

principle

Alan Turing (ca.1935)
Turing's slate sculpture with Enigma (next to his portrait on the wall)
The Turing bomb consists of a series of three sets of twelve Enigma rollers. The colors of the "drums" (English drums ) indicate the number of the corresponding roller
(roller I = red,
roller II = chestnut,
green roll III =,
roller IV = yellow,
roll V = light brown,
roller VI = blue,
roller VII = black,
roller VIII = silver).
The American high-speed version of the Turing bomb reached up to 2000 revolutions per minute, more than fifteen times the speed of its British model and was specifically directed against the four-roller Enigma
The Desch bomb in the National Cryptologic Museum is the only known original bomb from World War II.

The bomb , as the code breaker called short was based on the Polish Bomba : (see also compared the bombing with the Polish Bomba ) by the British mathematician Alan Turing devised and his colleague Gordon Welchman by introducing the diagonal board (German: Diagonal Board ) significantly improved ( Turing-Welchman bomb ). The involutorics (encryption = decryption) of the Enigma and especially the involutorics of your connector board are cryptanalytically used by connecting several Enigma machines in series within the Turing bomb . In this way, the influence of the plug board on the size of the key area can be removed and the search area can be drastically reduced.

The key you are looking for can be found by exhaustion (complete search of the key area). The method used here is designated with the Latin term Reductio ad absurdum (German: return to contradiction). It is based on the use of a probable word (English: crib ) whose occurrence in the text can be expected or at least assumed. Due to the known internal wiring of the Enigma's key rollers and their possible positions to each other, the observed or assumed relationships between the present ciphertext and the likely word of the plaintext can only be fulfilled under very specific conditions and only with very few keys. With the help of this method it is possible to exclude the vast majority of all keys and thus ultimately to find the correct daily Enigma key used by the Germans to encrypt their radio messages .

The bomb compares the text phrase ( crib ) accepted in the encrypted message with the corresponding ciphertext fragment and tries to decrypt the ciphertext fragment with all possible key settings for roller position and roller position. If the result of the decryption attempt matches the assumed Crib , then the key setting of the bomb used for this purpose may correspond to the daily key of the Enigma sought. While still appearing "miss", because of the shortness of the Cribs are quite possible, must be recognized by tentatively decoding of the remaining ciphertext and discarded. Once the Enigma's daily key is finally found, the entire ciphertext can easily be decrypted, as by the authorized recipient.

Instead of the number of "150 million million" possibilities mentioned in some popular scientific representations, feature films such as " Enigma - The Secret " and " The Imitation Game - A Top Secret Life ", or novels such as Enigma by the British writer Robert Harris that she has to work through is actually "only" 26³ (= 17576) times 60, ie 1,054,560 possibilities under which she has to find the "correct" position (see also: Chapter deciphering and key space in the overview article on the Enigma).

These approximately one million different cases are practically impossible to try out by hand in a reasonable amount of time. However, with the help of the Turing bomb , which was motorized at 64 revolutions per minute and could process 26 cases during each revolution, it only took 1,054,560 / (26 · 64) minutes, i.e. a little more than ten hours, to test all the possibilities. (In addition, there is the time to set and retool the machine for the sixty different roller positions, which doubles the time to around twenty hours.) If you make the effort to use sixty bombs , one for each roller position, the time for a run of a little more than ten hours to a good ten minutes - a tolerable time.

history

The first prototype of the Turing bomb , called Victory ( German  "Sieg" ), was completed in the spring of 1940 by the British engineer Harold Keen and his team of twelve employees from the British Tabulating Machine Company ( German  "British Tabulating Machine Company " ). The device, which was based on Turing's concept of the Letchworth Enigma , was subsequently used successfully in Bletchley Park to decipher German Enigma radio messages. After Gordon Welch Mans invention of the diagonal board ( German  "Diagonal Board" ) has been considerably improved the efficiency of the machine, production was significantly increased. With the close cooperation of the cryptanalyst Welchman and the electrical engineer Keen, twelve more copies were made by the end of 1941 under the code name " CANTAB " and more than 210 bombs by the end of the war .

The first fully operational Turing Welchman bomb (incl. Diagonal board ) was used in mid-August 1940. It was named "Agnes", possibly in honor of Agnes Meyer Driscoll , the American colleague of the British Codebreakers . It took Agnes about 15 minutes to exhaust a roller layer , a time that could be reduced to about six minutes in later models by increasing the speed of the drums. By the end of the war, more than 210 bombs were in operation in England alone.

In addition, under the direction of Joseph Desch in the United States Naval Computing Machine Laboratory (NCML) , which was based in the National Cash Register Company (NCR) in Dayton ( Ohio ), more than 120 high-speed variants were produced from April 1943, which specifically counteracted the Enigma-M4 used only by the German submarines were directed. In contrast to the other Enigma models with three rollers, the M4 used a fourth roller and was therefore "cracked" with correspondingly more complex so-called Desch bombs .

Name origin

The term bomb , which the British codebreakers used for their machine, is the French spelling of the English word "bomb" (German: bomb). It was chosen based on the Polish forerunner of the Turing bomb , the Bomba (Polish for bomb) developed by the Polish code breaker Marian Rejewski . The origin of this original name has not been clearly established.

After the war, even Rejewski couldn't remember how this name came about. People like to say that he and his colleagues Różycki and Zygalski had just eaten an ice bomb in a café while he was formulating the idea for the machine. Then Jerzy Różycki suggested this name. Another hypothesis is that the machine dropped a weight, similar to the way an airplane drops a bomb, and so clearly audibly signaled that a possible roller position had been found. A third variant assumes the operating noise of the machine, which is said to have resembled the ticking of a time bomb, as the reason for the name. The appearance of the machine, which is said to have resembled the typical hemispherical shape of an ice bomb, is also given as the origin of the name. Unfortunately, no bombs have survived, making it difficult to verify the various hypotheses of the name. Rejewski himself stated quite soberly that the name came about because they “couldn't think of anything better” (English: “For lack of a better name we called them bombs.” ).

In any case, the British in Bletchley Park took over the original Polish name and translated it into French. Possibly this has something to do with the fact that the Polish code breakers stayed in France in 1939 after the German attack on their country and their escape from Poland and communicated with the British from there.

Bomb replica project

Front view of the replica in Bletchley Park
Rear view of the replica in Bletchley Park

At the original location, in Bletchley , about 70 km north-west of London , the bomb reconstruction project (English original title: The Turing Bombe Rebuild Project ) ran for more than ten years from 1995 . A team of up to 60 volunteers led by John Harper set the goal of recreating a Turing bomb as true to the original as possible. This succeeded and on July 17, 2007, in a small ceremony in the presence of John Harper and some former Wrens (female members of the Navy who had operated the bombs during the war ), the fully functional replica of a Turing bomb was launched by Edward, the Duke of Kent , officially put into operation. It is exhibited at the original location and open to the public.

Cinematic reception

Roller set of a replica of the Turing bomb

Turing bombs in action can be seen in the British feature film Enigma , which is based on the novel Enigma and deals with the deciphering work of the British code breakers from Bletchley Park. The bombs are replicas that are not fully functional, but represent the external appearance and especially the rotating drums realistically. The work of the code breakers in creating the “menus” necessary for the bomb is also shown very successfully. The various radio messages have been realistically generated and encrypted especially for the film according to the original rules and procedures.

The 2014 British-American co-production The Imitation Game illustrates the life and contributions of Alan Turing as a code breaker in Bletchley Park. The special focus is on the development history of "his" bomb , the construction and operation of which are clearly illustrated.

literature

  • Chris Christensen: Review of IEEE Milestone Award to the Polish Cipher Bureau for `` The First Breaking of Enigma Code '' . Cryptologia . Rose-Hulman Institute of Technology. Taylor & Francis, Philadelphia PA 39.2015,2, pp. 178-193. ISSN  0161-1194 .
  • Donald W. Davies: The bomb - A remarkable logic machine. Cryptologia . Rose-Hulman Institute of Technology. Taylor & Francis, Philadelphia PA 23.1999,2, pp. 108-138. ISSN  0161-1194 .
  • David P. Mowry: German Cipher Machines of World War II (PDF; 1.1 MB) . Center for Cryptologic History, National Security Agency, Fort Meade 2003. 36 pp.
  • Jennifer Wilcox: Solving the Enigma - History of the Cryptanalytic Bombe . Center for Cryptologic History, National Security Agency, Fort Meade 2001.
  • John Wright: The Turing Bombe Victory and the first naval Enigma decrypts . Cryptologia, 2016. doi: 10.1080 / 01611194.2016.1219786

Web links

Commons : Turing bomb  - collection of pictures, videos and audio files

Individual evidence

  1. ^ 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
  2. ↑ The US 6812 Bomb Report 1944 . 6812th Signal Security Detachment, APO 413, US Army. Publication, Tony Sale, Bletchley Park, 2002. p. 9. Accessed March 16, 2010. PDF; 1.3 MB
  3. ↑ John AN Lee, Colin Burke, Deborah Anderson: The US Bombes, NCR, Joseph Desch, and 600 WAVES - The first Reunion of the US Naval Computing Machine Laboratory . IEEE Annals of the History of Computing, 2000. p. 35. Accessed: May 21, 2008. PDF; 0.5 MB ( Memento from February 21, 2007 in the Internet Archive )
  4. ↑ Impact Of Bombe On The War Effort , accessed May 23, 2018.
  5. ↑ Robert Harris: Enigma . Novel. Weltbild, Augsburg 2005, p. 71. ISBN 3-89897-119-8
  6. ↑ The US 6812 Bomb Report 1944 . 6812th Signal Security Detachment, APO 413, US Army. Publication, Tony Sale, Bletchley Park, 2002. p. 59. Accessed January 7, 2014. PDF; 1.3 MB
  7. ^ Hugh Sebag-Montefiore: Enigma - The battle for the code . Cassell Military Paperbacks, London 2004, p. 235. ISBN 0-304-36662-5
  8. ↑ Michael Miller: Symmetrical Encryption Methods - Design, Development and Cryptanalysis of Classic and Modern Ciphers . Teubner, April 2003, p. 70. ISBN 3-519-02399-7
  9. ↑ Friedrich L. Bauer: Deciphered secrets. Methods and maxims of cryptology. 3rd, revised and expanded edition. Springer, Berlin et al. 2000, p. 423.
  10. ^ Gordon Welchman: The Hut Six Story - Breaking the Enigma Codes . Allen Lane, London 1982; Cleobury Mortimer M&M, Baldwin Shropshire 2000, p. 81. ISBN 0-947712-34-8 .
  11. ^ Hugh Sebag-Montefiore: Enigma - The battle for the code . Cassell Military Paperbacks, London 2004, p. 345. ISBN 0-304-36662-5 .
  12. ↑ a b Kris Gaj, Arkadiusz Orłowski: Facts and myths of Enigma: breaking stereotypes. Eurocrypt, 2003, p. 121ff.
  13. ↑ 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 , p. 431.
  14. ^ A b Hugh Sebag-Montefiore: Enigma - The battle for the code . Cassell Military Paperbacks, London 2004, p. 46. ISBN 0-304-36662-5
  15. ↑ Simon Singh: Secret Messages . Carl Hanser Verlag, Munich 2000, p. 194. ISBN 0-89006-161-0
  16. ↑ 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 , p. 419.
  17. ^ Marian Rejewski: How Polish Mathematicians Deciphered the Enigma . Annals of the History of Computing, Vol. 3, No. 3, July 1981, p. 226.
  18. ↑ Enigma replica 'homage to heroes' (English). Retrieved June 29, 2016.
  19. ↑ The Royal Switch on ( Memento of August 28, 2009 in the Internet Archive ) (English)
  20. ↑ Robert Harris: Enigma . Novel. Weltbild, Augsburg 2005. ISBN 3-89897-119-8
  21. ^ Tony Sale: Making the Enigma ciphers for the film "Enigma" . Retrieved March 26, 2008.