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The Colossus was the first programmable (to a limited extent) digital electronic computer, used for breaking German Fish Cyphers, especially the Lorenz cipher. It was designed by Max Newman and associates of Bletchley Park, and was built by the British Post Office Research Station at Dollis Hill, by Tommy Flowers and crew.Colossus was preceded by several computers, many first in some category. Zuse's Z3 was the world's first functional fully program-controlled computer, and was based on electromechanical relays, as were the (less advanced) Bell Labs machines of the late 1930s (George Stibitz, et al). The Atanasoff Berry Computer of circa 1937 was electronic and arguably the first working digital computer, but wasn't programmable. Assorted analog computers were semiprogrammable, some of these much predated the 1930s (eg, Vannevar Bush). Babbage's Analytical engineThe analytical engine an important step in the history of computers, is the design of a mechanical, modern general purpose computer by the British professor of mathematics Charles Babbage. It was first described in 1837, but Babbage continued to work on h antedated all these (in the mid-1800s), and was both digital and programmable, but was only partially constructed and never functioned at the time (a replica of his Difference engine No. 2For the novel by William Gibson, see The Difference Engine A Difference engine is a mechanical special-purpose computer designed to tabulate polynomial functions. Since logarithmic and trigonometric functions can be approximated by polynomials, such a mac, built in 1991 does work, however). Colossus was the first combining all of digital, (partially) programmable, and electronic.
1 Purpose
The Colossus was primarily designed for cryptanalysisCryptanalysis (from the Greek kryptos and analyein "to loosen" or "to untie") is the study of methods for obtaining the meaning of encrypted information without access to the secret information which is normally required to do so. Typically, this involves in an attempt to break one of the Fish cyphers (a Bletchley Park term) used by the German military for its most secure strategic communications. These were teletype cypher machines in the spirit of that first proposed by Colonel Parker Hitt of the US Army around WWI. The GermanThe Federal Republic of Germany ( German: Bundesrepublik Deutschland is one of the world's leading industrialized countries, located in the middle of the European Union. It is bordered to the north by the North Sea, Denmark and the Baltic Sea, to the east machines were, essentially, attempts at an electromechanical implementation of the one-time pad cypher invented by Gilbert Vernam (Bell Labs) and Joseph Mauborgne (Signal Corps, USA) in the US at the end of WWI. The most important was a teletype based machine built by Lorenz Electric , the SZ-40 (and later SZ-42) Schlüsselzusatz (meaning, more or less, 'auxiliary key').
Another, different, teletype cypher machine was designed and built by Siemens & Halske, the T-52 Geheimfernschreiber (meaning, 'secret teleprinter'). Early versions of the Siemens machine (the T-52a and T-52b) were used to send signals between Germany and Norway over a cable running through Sweden. The Swedes tapped the cable, copied the traffic, and Arne Beurling, a Swedish mathematician, broke the cypher. Later production versions of the T-52 (there were variants through 'e') were considerably more secure, and quite hard to break even for Bletchley Park. Some of the T-52 traffic was also sent over Luftwaffe Enigma networks which were much more easily broken, and so T-52 traffic was a lower priority for Bletchley Park than might have otherwise been expected.
The one-time pad requires a random sequence. It is combined with the plaintext (bit by bit, usually as character by character) resulting in the cyphertext which is transmitted. On receipt, the same random sequence is combined with the cyphertext (again usually character by character), and because the combining operation is reversible in a particular way (see XOR, for example) the output is the original plaintext. In the German Fish machines, the 'random' sequence was produced by various electromechanical arrangements (on one of them, these were rotors somewhat as in the US SIGABA machine), and the sequence wasn't actually random. Because there were patterns, they could be predicted if the cryptanalysts were sufficiently clever, and plaintexts thereupon recovered. In the case of the Lorenz machine, Col John Tiltman and Bill Tutte of Bletchley Park were sufficiently clever. In the case of the early Siemens machine, Beurling had been sufficiently clever.
