Leslie Yoxall

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Albert Leslie Yoxall (born  May 18, 1914 in Salford , †  September 30, 2005 ) was an English cryptanalyst . During the Second World War he played a major role in the Government Code and Cypher School (GC&CS) in Bletchley Park , England , the military service that successfully deciphered German communications contributed to the breakage of the German rotor key machine Enigma . He developed a method specifically for the cryptanalytical attack on double- encrypted Enigma radio messages ("officer procedure"), which he called "Yoxallism" in his honor . After the war, he worked for the Government Communications Headquarters (GCHQ) , the successor organization of GC&CS , until the mid-1970s .

Life

youth

Yoxall was born in the English city of Salford (west of Manchester ) as the youngest of four brothers who lost their father in a tram accident at a young age. He attended Manchester Grammar School (MGS) , a primary school for boys in Manchester before moving to in 1933 Cambridge at the Sidney Sussex College , an educational institution of the University of Cambridge , joined and his training in 1941 with a doctorate degree Ph. D. completed.

Bletchley Park

When the Second World War broke out, he was already working as a math teacher at "his" Manchester Grammar School , where in April 1941 one of the leading minds of the British code breakers from Bletchley Park (BP), the English mathematician and cryptanalyst Gordon Welchman , recruited him. After interviews with Alan Turing and Hugh Alexander , Yoxall was assigned to Hut 8 (German: Baracke 8), i.e. the organizational unit of BP which, under the direction of Alan Turing and his deputy Stuart Milner-Barry, deals with the deciphering of radio messages from the German Navy who used the Enigma-M3 and Enigma-M4 for encryption .

So-called “officer radio messages” turned out to be particularly difficult to “crack” because the Germans encrypted them twice using their encryption machine. For this purpose, Yoxall developed a special procedure that became known in his honor in BP under the name "Yoxallism", and with the help of which it was possible to successfully decipher radio messages from officers. The British code breakers from Bletchley Park succeeded in maintaining the Enigma's ability to decipher, with the exception of a few interruptions, for the entire period of the war and thus contributed significantly to the rapid victory of the Allies.

Towards the end of 1942, after the Enigma had already become routine, Yoxall switched to Hut 7 (German: Baracke 7), which dealt with Japanese naval codes. There he made a valuable contribution in connection with the analysis of the Japanese key permutations.

After the war

In 1949 he married Doris Gibson and spent several years as a writer in the London district of Eastcote . In 1953 he joined the Government Communications Headquarters in Cheltenham , the successor organization to GC&CS , in whose service he was active from 1959 to 1963 and again from 1968 to 1972 as a British liaison officer in the US capital Washington . He finished his work at the GCHQ in 1974 and then worked again as a math teacher for some time.

Leslie Yoxall died at the age of 91 after losing his wife Doris three years earlier. They didn't have any children.

literature

Web links

  • Photo (accessed March 10, 2015)

Individual evidence

  1. ↑ a b Obituary for Leslie Yoxall "Mathematician who helped to break wartime German Enigma codes at Bletchley Park" in Times Online of October 27, 2005. Accessed: March 8, 2010.
  2. ^ Geoff Sullivan, Frode Weierud: Breaking German Army Ciphers . Cryptologia , Vol XXIX (3), July 2005, pp. 217-219 PDF; 6.1 MB
  3. ^ Hugh Sebag-Montefiore: Enigma - The battle for the code . Cassell Military Paperbacks, London 2004, p. 296. ISBN 0-304-36662-5
  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
personal data
SURNAME Yoxall, Leslie
ALTERNATIVE NAMES Yoxall, Albert Leslie
BRIEF DESCRIPTION British cryptologist
DATE OF BIRTH May 18, 1914
PLACE OF BIRTH Salford
DATE OF DEATH September 30, 2005