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Heath Robinson (codebreaking machine)
Heath Robinson was a machine used by British codebreakers at the Government Code and Cypher School (GC&CS) at Bletchley Park during World War II in Cryptanalysis of the Lorenz cipher. This achieved the decryption of messages in the German teleprinter cipher produced by the Lorenz SZ40/42 in-line cipher machine. Both the cipher and the machines were called "Tunny" by the codebreakers, who named different German teleprinter ciphers after fish. It was mainly an electro-mechanical machine, containing no more than a couple of dozen valves (vacuum tubes), and was the predecessor to the electronic Colossus computer. It was dubbed "Heath Robinson" by the Wrens who operated it, after cartoonist William Heath Robinson, who drew immensely complicated mechanical devices for simple tasks, similar to Rube Goldberg in the USA.
The functional specification of the machine was produced by Max Newman. The main engineering design was the work of Frank Morrell at the Post Office Research Station at Dollis Hill in North London, with his colleague Tommy Flowers designing the "Combining Unit".〔 Dr C. E. Wynn-Williams from the Telecommunications Research Establishment at Malvern produced the high-speed electronic valve and relay counters.〔 in ''1. Introduction: Some historical notes''〕 Construction started in January 1943, the prototype machine was delivered to Bletchley Park in June and was first used to help read current encrypted traffic soon afterwards.〔 in ''3. Organisation: Machine Setting Organisation''〕
==Tutte's statistical method==
The basis of the method that the Heath Robinson machine implemented was Bill Tutte's "1+2 technique". This involved examining the first two of the five impulses〔"Impulse" is the term used at Bletchley Park. Today one would say "the first two bits".〕 of the characters of the message on the ciphertext tape and combining them with the first two impulses of part of the key as generated by the ''chi'' wheels of the Lorenz machine. This involved reading two long loops of paper tape, one containing the ciphertext and the other the ''chi'' component of the key. By making the key tape one character longer than the message tape, each of the 1271 starting position of the ''chi''1 ''chi''2 sequence was tried against the message. A count was amassed for each start position and, if it exceeded a pre-defined "set total", was printed out. The highest count was the most likely one to be the one with the correct values of ''chi''1 and ''chi''2. With these values, settings of the other ''chi'' wheels could be tried to break all five ''chi'' wheel starting positions for this message. This then allowed the effect of the ''chi'' component of the key to be removed and the resulting modified message attacked by manual methods in the Testery.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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