Alan Turing

Cryptanalysis

Two cottages in the stable yard at Bletchley Park. Turing worked here from 1939–1940 until he moved to Hut 8.During World War II, Turing was a major participant in the efforts at Bletchley Park to break German ciphers. Building on cryptanalysis work carried out in Poland prior to the outbreak of war, he contributed several insights into breaking both the Enigma machine and the Lorenz SZ 40/42 (a teletype cipher attachment codenamed "Tunny" by the British), and was, for a time, head of Hut 8, the section responsible for reading German Naval signals.

Since September 1938, Turing had been working part-time for the Government Code and Cypher School. Turing reported to Bletchley Park on 4 September 1939, the day after Britain declared war on Germany.[1]


The Turing-Welchman bombe

Replica of a bombe machineWithin weeks of arriving at Bletchley Park,[1] Turing had devised an electromechanical machine which could help break Enigma: the bombe, named after the Polish-designed bomba. The bombe, with an enhancement suggested by mathematician Gordon Welchman, became the primary tool used to read Enigma traffic.

The bombe searched for the correct settings of the Enigma rotors, and required a suitable "crib": a piece of matching plaintext and ciphertext. For each possible setting of the rotors, the bombe performed a chain of logical deductions based on the crib, implemented electrically. The bombe detected when a contradiction had occurred, and ruled out that setting, moving onto the next. Most of the possible settings would cause contradictions and be discarded, leaving only a few to be investigated in detail. Turing's bombe was first installed on 18 March 1940Template:Hodges, 1983, p. 191. Over 200 bombes were in operation by the end of the war[citation needed].


Hut 8 and Naval Enigma
In December 1940, Turing solved the naval Enigma indicator system, which was more complex than the indicator systems used by the other services. Turing also invented a Bayesian statistical technique termed "Banburismus" to assist in breaking Naval Enigma. Banburismus could rule out certain orders of the Enigma rotors, reducing time needed to test settings on the bombes.

In the spring of 1941, Turing proposed marriage to fellow Hut 8 co-worker Joan Clarke, although the engagement was broken off by mutual agreement in the summer.

In July 1942, Turing devised a technique termed Turingismus or Turingery for use against the Lorenz cipher. A frequent misconception is that Turing was a key figure in the design of the Colossus computer; this was not the case.[2]

Turing travelled to the United States in November 1942 and liaised with US Navy cryptanalysts on Naval Enigma and bombe construction in Washington, and assisted at Bell Labs with the development of secure speech devices. He returned to Bletchley Park in March 1943. During his absence, Hugh Alexander had assumed the position of head of Hut 8, although Alexander had been de facto head for some time, Turing having little interest in the day-to-day running of the section. Turing became a general consultant for cryptanalysis at Bletchley Park.

In the latter part of the war, teaching himself electronics at the same time, Turing undertook (assisted by engineer Donald Bayley) the design of a portable machine codenamed Delilah to allow secure voice communications. Intended for different applications, Delilah lacked capability for use with long-distance radio transmissions, and was completed too late to be used in the war. Though Turing demonstrated it to officials by encrypting/decrypting a recording of a Winston Churchill speech, Delilah was not adopted for use.

In 1945, Turing was awarded the OBE for his wartime services.


Early computers and the Turing Test

Turing achieved world-class Marathon standards. His best time of 2 hours, 46 minutes, 3 seconds,[citation needed] was only 11 minutes slower than the winner in the 1948 Olympic Games.From 1945 to 1947 he was at the National Physical Laboratory, where he worked on the design of ACE (Automatic Computing Engine). He presented a paper on February 19, 1946, which was the first complete design of a stored-program computer in Britain. Although he succeeded in designing the ACE, there were delays in starting the project and he became disillusioned. In late 1947 he returned to Cambridge for a 'sabbatical' year. While he was at Cambridge, ACE was completed in his absence and executed its first program on May 10, 1950. In 1949 he became deputy director of the computing laboratory at the University of Manchester, and worked on software for one of the earliest true computers — the Manchester Mark I. During this time he continued to do more abstract work, and in "Computing machinery and intelligence" (Mind, October 1950), Turing addressed the problem of artificial intelligence, and proposed an experiment now known as the Turing test, an attempt to define a standard for a machine to be called "sentient".

In 1948, Turing, working with his former undergraduate colleague, D.G. Champernowne, began writing a chess program for a computer that did not yet exist. In 1952, lacking a computer powerful enough to execute the program, Turing played a game in which he simulated the computer, taking about half an hour per move. The game was recorded; the program lost to a colleague of Turing, Alick Glennie, however, it is said that the program won a game against Champernowne's wife.


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