One tape contained the ciphertext in a continuous loop. It had two punched paper tapes that had to work exactly together. The first machine was called "Heath Robinson". The start position that gave the largest count from this calculation was likely to be the right one. The machine would do a calculation for many possible start positions of the χ wheels. He was given the job of working out how a machine could break "Tunny" messages. Max Newman was a mathematician and codebreaker at Bletchley Park. Whether or not the ψ wheels moved on was controlled by two wheels that he called two the μ ("mu") or "motor wheels". The ψ wheels, however, did not move regularly. He worked out that the χ wheels moved on one position for each new character coded. He called one set of five the χ ("chi") wheels, and the other set of five the ψ ("psi") wheels. He used Greek letters to name the wheels. Tutte worked out that the machine made each keystream character by combining the effects of two sets of five wheels. This work has been described as "the greatest intellectual achievement of world war II". After a lot of work he succeeded, and produced a logical description of the unseen machine. They were then joined by a young codebreaker called Bill Tutte who was given the job. The codebreakers tried to work out the details of the machine from this information, but at first they failed. There were a total of 501 cams each of which could be put into the raised (active) position or the lowered (inactive) position. It had ten wheels each with a different number of cams. It was not seen by the Allies until the end of WWII when they learnt that it was the Lorenz SZ42. The Germans used it to code secret teleprinter communications. The machine that was code named "Tunny" by the British. A codebreaker called John Tiltman was able to get the keystream from these messages. This mistake was very useful to the research codebreakers. On 30 August 1941 two versions of the same message, which was nearly 4,000 characters long, were sent with the same wheel start positions. If the German operators always worked correctly, no two messages would have the same start position of the wheels. ![]() At the receiving end an identical machine removed the keystream to produce the plaintext of the message. The ciphertext, which made no sense, was transmitted by radio. The coding machine added together the plaintext (the un-coded version of the message) and a stream of characters (letters, numbers, punctuation) called the keystream (a stream of seemingly random characters) that it generated to make the ciphertext (the coded version of the message). The total number of possible start positions of the 12 wheels was very large indeed. He told the operator who was receiving the message what the start positions were with 12 letters that were not coded. The start position for the message was chosen by the operator who was sending the message. For each new message sent, the wheels had first to be turned to new positions. Their research also showed that the coding was being done by a rotor cipher machine with 12 wheels (rotors). The British codebreakers saw that it used a five-unit code like a teleprinter system. Regular radio transmissions of "Tunny" messages started in June 1941. The output from Colossus was then worked on by people who had a very good knowledge of the German language. It just found likely settings of the machine. Colossus did not perform all of the decoding process. When Colossus found likely settings for two wheels, the codebreaker designed further programs for Colossus until likely settings of other wheels were found. It tried various possibilities of how two of the wheels had been set up. Colossus imitated the machine and read the coded message from a punched tape. ![]() ![]() They called the machine and its coded messages "Tunny". The messages had been coded by an unknown German machine. Ten Colossus computers were in use at the end of the war.īritish codebreakers called the teleprinter messages "Fish". ![]() It first worked on 1 June 1944, just before the Normandy Landings on D-Day. The first machine, Mark 1, worked in December 1943 and solved its first problem in February 1944. Their design, which was called "Colossus" used many vacuum tubes (valves). A group of Post Office telephone engineers led by Tommy Flowers worked out how to do this. His problem was how to get a machine that would help turn German coded radio teleprinter messages into ordinary language. Reading these messages helped the Allies to win the war.Ĭodebreaker Max Newman worked at the Government Code and Cypher School (GC&CS) at Bletchley Park. These messages were sent between the German High Command, and army field commanders. British code breakers used Colossus for cryptanalysis during World War II. A Colossus computer as it was during World War IIĬolossus was the world's first programmable electronic digital computer.
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