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Turingery〔 in ''Testery Methods 1942-1944''〕 or Turing's Method (playfully dubbed Turingismus by Peter Ericsson, Peter Hilton and Donald Michie) was a hand codebreaking method devised in July 1942〔 in ''Early Hand Methods''〕 by the mathematician and cryptanalyst Alan Turing at the British Government Code and Cypher School at Bletchley Park during World War II. It was for use in Cryptanalysis of the Lorenz cipher produced by the SZ40 and SZ42 teleprinter rotor stream cipher machines, one of the Germans' ''Geheimschreiber'' (secret writer) machines. The British codenamed non-Morse traffic "Fish", and that from this machine "Tunny". Reading a Tunny message required firstly that the logical structure of the system was known, secondly that the periodically changed pattern of active cams on the wheels was derived, and thirdly that the starting positions of the scrambler wheels for this message—the message key—was established. The logical structure of Tunny had been worked out by William Tutte and colleagues over several months ending in January 1942. Deriving the message key was called "setting" at Bletchley Park, but it was the derivation of the cam patterns—which was known as "wheel breaking"—that was the target of Turingery. German operator errors in transmitting more than one message with the same key, producing a "depth", allowed the derivation of that key. Turingery was applied to such a key stream to derive the cam settings. ==The SZ40 and SZ42== (詳細はrotor cipher machines which implemented a Vernam stream cipher. They were attached in-line to standard Lorenz teleprinters. The message characters were encoded in the 5-bit International Telegraphy Alphabet No. 2 (ITA2). The output ciphertext characters were generated by combining a pseudorandom character-by-character key stream with the input characters using the "exclusive or (XOR)" function (symbolised by ⊕ ). ::::: Plaintext ⊕ Key = Ciphertext Similarly, for deciphering, the ciphertext was combined with the same key to give the plaintext. ::::: Ciphertext ⊕ Key = Plaintext This produces the essential reciprocity to allow the same machine with the same settings to be used for both enciphering and deciphering. Each of the five bits of the key for each character was generated by the relevant wheels in two parts of the machine. These were termed the ''chi'' () wheels, and the ''psi'' () wheels. The ''chi'' wheels all moved on one position for each character. The ''psi'' wheels also all moved together, but not after each character. Their movement was controlled by the two ''mu'' () or "motor" wheels.〔 in ''German Tunny''〕 The key stream generated by the SZ machines thus had a ''chi'' component and a ''psi'' component that were combined together with the XOR function. So, the key that was combined with the plaintext for enciphering—or with the ciphertext for deciphering—can be represented as follows.〔 ::::: Key = ''Chi''-Key ⊕ ''Psi''-Key Symbolically: ::::: K = ⊕ The twelve wheels each had a series of cams (or "pins") around them. These cams could be set in a raised or lowered position. In the raised position they generated a "mark" ' x ' (1 in binary), in the lowered position they generated a "space" ' • ' (0 in binary). The number of cams on each wheel equalled the number of impulses needed to cause them to complete a full rotation. It should be noted that these numbers are all co-prime with each other, giving the longest possible time before the pattern repeated. With a total of 501 cams this equals 2501 which is approximately 10151, an astronomically large number. However, if the five impulses are considered independently, the numbers are much more manageable. The product of the rotation period of any pair of ''chi'' wheels gives numbers between 41×31=1271 and 26×23=598. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Turingery」の詳細全文を読む スポンサード リンク
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