![]() This was achieved by "differencing" in which each bit or character was XOR-ed with its successor. ![]() However, the cryptanalysts worked out that by examining the frequency distribution of the character-to-character changes in the ciphertext, instead of the plain characters, there was a departure from uniformity which provided a way into the system. With a sufficiently random keystream, a Vernam cipher removes the natural language property of a plaintext message of having an uneven frequency distribution of the different characters, to produce a uniform distribution in the ciphertext. An active cam reversed the value of a bit (0→1 and 1→0). Cams on wheels 9 and 10 showing their raised (active) and lowered (inactive) positions. The chi wheels stepped regularly with each letter that was encrypted, while the psi wheels stepped irregularly, under the control of the motor wheels. He deduced that the twelve wheels consisted of two groups of five, which he named the χ ( chi) and ψ ( psi) wheels, the remaining two he called μ ( mu) or "motor" wheels. ![]() Then Bill Tutte, a newly arrived member of the Research Section, used this keystream to work out the logical structure of the Lorenz machine. First, John Tiltman, a very talented GC&CS cryptanalyst, derived a key stream of almost 4000 characters. These were intercepted and worked on at Bletchley Park. In August 1941, a blunder by German operators led to the transmission of two versions of the same message with identical machine settings. It did this by combining the plaintext characters with a stream of key characters using the XOR Boolean function to produce the ciphertext. It was deduced that the machine had twelve wheels and used a Vernam ciphering technique on message characters in the standard 5-bit ITA2 telegraph code. īefore the Germans increased the security of their operating procedures, British cryptanalysts diagnosed how the unseen machine functioned and built an imitation of it called " British Tunny". This led the British to call encrypted German teleprinter traffic " Fish", and the unknown machine and its intercepted messages " Tunny" (tunafish). Intelligence information revealed that the Germans called the wireless teleprinter transmission systems "Sägefisch" (sawfish). The Colossus computers were used to help decipher intercepted radio teleprinter messages that had been encrypted using an unknown device. See also: Cryptanalysis of the Lorenz cipher A Lorenz SZ42 cipher machine with its covers removed at The National Museum of Computing on Bletchley Park The Lorenz SZ machines had 12 wheels, each with a different number of cams (or "pins"). A functioning rebuild of a Mark 2 Colossus was completed in 2008 by Tony Sale and a team of volunteers it is on display at The National Museum of Computing on Bletchley Park. The two retained machines were eventually dismantled in the 1960s. All but two machines were dismantled into such small parts that their use could not be inferred. The existence of the Colossus machines was kept secret until the mid-1970s. Bletchley Park's use of these machines allowed the Allies to obtain a vast amount of high-level military intelligence from intercepted radiotelegraphy messages between the German High Command ( OKW) and their army commands throughout occupied Europe. Ten Colossi were in use by the end of the war and an eleventh was being commissioned. An improved Colossus Mark 2 that used shift registers to quintuple the processing speed, first worked on 1 June 1944, just in time for the Normandy landings on D-Day. The prototype, Colossus Mark 1, was shown to be working in December 1943 and was in use at Bletchley Park by early 1944. (Turing's machine that helped decode Enigma was the electromechanical Bombe, not Colossus.) It has sometimes been erroneously stated that Turing designed Colossus to aid the cryptanalysis of the Enigma. Alan Turing's use of probability in cryptanalysis (see Banburismus) contributed to its design. Ĭolossus was designed by General Post Office (GPO) research telephone engineer Tommy Flowers to solve a problem posed by mathematician Max Newman at the Government Code and Cypher School (GC&CS) at Bletchley Park. Colossus is thus regarded as the world's first programmable, electronic, digital computer, although it was programmed by switches and plugs and not by a stored program. Colossus used thermionic valves (vacuum tubes) to perform Boolean and counting operations. Paper tape of up to 20,000 × 5-bit characters in a continuous loopĬolossus was a set of computers developed by British codebreakers in the years 1943–1945 to help in the cryptanalysis of the Lorenz cipher. A total of 1,600 in Mk 1 and 2,400 in Mk 2.
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