Alan Turing

Alan Mathison Turing (June 23, 1912 – June 7, 1954) was a British mathematician, logician, and cryptographer.

Cryptanalysis

During World War II, Turing was a major participant in the efforts at Bletchley Park to break German ciphers. Turing's codebreaking work was kept secret until the 1970s; not even his close friends knew about it. He contributed several mathematical 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.

Related Topics:
World War II - Bletchley Park - 1970s - Enigma machine - Lorenz SZ 40/42

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Since September 1938, Turing had been recruited to work part-time for the Government Code and Cypher School. Turing reported to Bletchley Park when war was declared in September 1939. To break Enigma, Turing devised an electromechanical machine which searched for the correct settings of the Enigma rotors. The machine was called the bombe, named after the Polish-designed bomba. Using a bombe, it was possible to ignore the effect of the Enigma plugboard and consider the settings of its rotors alone, and eliminate most of them from consideration. For each possible setting, a chain of logical deductions was implemented electrically, and it was possible to detect when a contradiction had occurred and rule out that setting. Turing's bombe was first installed on 18 March 1940, and, with an enhancement suggested by mathematician Gordon Welchman, was the primary tool used to read Enigma traffic. Over 200 bombes were in operation by the end of the war.

Related Topics:
1938 - Government Code and Cypher School - Bletchley Park - 1939 - Bombe - Bomba - 18 March - 1940 - Gordon Welchman

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

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. Against the Lorenz cipher, Turing devised a technique termed Turingismus or Turingery, although other methods were also used.

Related Topics:
1940 - Bayesian - Banburismus

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

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 November 1942, Turing visited the US to work on secure speech devices and Naval Enigma, returning 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.

Related Topics:
Secure speech - Hugh Alexander

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

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

Related Topics:
Delilah - Secure voice - Winston Churchill

~ ~ ~ ~ ~ ~ ~ ~ ~ ~