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applied cryptography - protocols, algorithms, and source code in c

As complicated as the enigma was it was broken during

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Unformatted text preview: rotors and the gears moving them that makes the machine secure. Because the rotors all move at different rates, the period for an n-rotor machine is 26n. Some rotor machines can also have a different number of positions on each rotor, further frustrating cryptanalysis. The best-known rotor device is the Enigma. The Enigma was used by the Germans during World War II. The idea was invented by Arthur Scherbius and Arvid Gerhard Damm in Europe. It was patented in the United States by Arthur Scherbius [1383]. The Germans beefed up the basic design considerably for wartime use. The German Enigma had three rotors, chosen from a set of five, a plugboard that slightly permuted the plaintext, and a reflecting rotor that caused each rotor to operate on each plaintext letter twice. As complicated as the Enigma was, it was broken during World War II. First, a team of Polish cryptographers broke the German Enigma and explained their attack to the British. The Germans modified their Enigma as the war progressed, and the British continued to cryptanalyze the new versions. For explanations of how rotor ciphers work and how they were broken, see [794,86,448,498,446,880,1315,1587,690]. Two fascinating accounts of how the Enigma was broken are [735,796]. Further Reading This is not a book about classical cryptography, so I will not dwell further on these subjects. Two excellent precomputer cryptology books are [587,1475]; [448] presents some modern cryptanalysis of cipher machines. Dorothy Denning discusses many of these ciphers in [456] and [880] has some fairly complex mathematical analysis of the same ciphers. Another older cryptography text, which discusses analog cryptography, is [99]. An article that presents a good overview of the subject is [579]. David Kahn’s historical cryptography books are also excellent [794,795,796]. 1.4 Simple XOR XOR is exclusive-or operation: ‘^’ in C or • in mathematical notation. It’s a standard operation on bits: 0•0=0 0•1=1 1•0=1 1•1=0 Also note that: a•a=...
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