I. J. Good
I. J. Good
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I. J. Good

Irving John Good (9 December 1916 – 5 April 2009) was a British mathematician who worked as a cryptologist at Bletchley Park with Alan Turing. After the Second World War, Good continued to work with Turing on the design of computers and Bayesian statistics at the University of Manchester. Good moved to the United States where he was a professor at Virginia Tech.

He was born Isadore Jacob Gudak to a Polish Jewish family in London. He later anglicised his name to Irving John Good and signed his publications "I. J. Good."

An originator of the concept known as the intelligence explosion, Good served as consultant on supercomputers to Stanley Kubrick, director of the 1968 film 2001: A Space Odyssey.

Good was born Isadore Jacob Gudak to Polish Jewish parents in London. His father was a watchmaker, who later managed and owned a successful fashionable jewellery shop, and was also a notable Yiddish writer writing under the pen name of Moshe Oved. Good was educated at the Haberdashers' Aske's Boys' School, at the time in Hampstead in northwest London, where, according to Dan van der Vat, Good effortlessly outpaced the mathematics curriculum.

Good studied mathematics at Jesus College, Cambridge, graduating in 1938 and winning the Smith's Prize in 1940. He did research under G. H. Hardy and Abram Besicovitch before moving to Bletchley Park in 1941 on completing his doctorate.

On 27 May 1941, having just obtained his doctorate at Cambridge, Good walked into Hut 8, Bletchley's facility for breaking German naval ciphers, for his first shift. This was the day that Britain's Royal Navy destroyed the German battleship Bismarck after it had sunk the Royal Navy's HMS Hood. Bletchley had contributed to Bismarck's destruction by discovering, through wireless-traffic analysis, that the German flagship was sailing for Brest, France, rather than Wilhelmshaven, from which she had set out. Hut 8 had not, however, been able to decrypt on a current basis the 22 German Naval Enigma messages that had been sent to Bismarck. The German Navy's Enigma cyphers were considerably more secure than those of the German Army or Air Force, which had been well penetrated by 1940. Naval messages were taking three to seven days to decrypt, which usually made them operationally useless for the British. This was about to change, however, with Good's help.

Alan Turing... had caught Good sleeping on the floor while on duty during his first night shift. At first, Turing thought Good was ill, but he was cross when Good explained that he was just taking a short nap because he was tired. For days afterwards, Turing would not deign to speak to Good, and he left the room if Good walked in. The new recruit only won Turing's respect after he solved the bigram tables problem. During a subsequent night shift, when there was no more work to be done, it dawned on Good that there might be another chink in the German indicating system. The German telegraphists had to add dummy letters to the trigrams which they selected out of the Kenngruppenbuch... Good wondered if their choice of dummy letters was random, or whether there was a bias towards particular letters. After inspecting some messages which had been broken, he discovered that there was a tendency to use some letters more than others. That being the case, all the codebreakers had to do, was to work back from the indicators given at the beginning of each message, and apply each bigram table in turn in the same way as Joan Clarke had done before. The bigram table which produced one of the popular dummy letters was probably the correct one. When Good mentioned his discovery to Alan Turing, Turing was very embarrassed, and said, 'I could have sworn that I tried that.' It quickly became an important part of the Banburismus procedure. Jack Good's refusal to go on working when tired was vindicated by a subsequent incident. During another long night shift, he had been baffled by his failure to break a doubly enciphered Offizier message. This was one of the messages which was supposed to be enciphered initially with the Enigma set up in accordance with the Offizier settings, and subsequently with the general Enigma settings in place. However, while he was sleeping before returning for another shift, he dreamed that the order had been reversed; the general settings had been applied before the Offizier settings. Next day he found that the message had yet to be read, so he applied the theory which had come to him during the night. It worked; he had broken the code in his sleep.

Good served with Turing for nearly two years. Subsequently, he worked with Donald Michie in Max Newman's group on the Fish ciphers, leading to the development of the Colossus computer.

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