The bombes were built by the British Tabulating Machine company at Letchworth. Each British bombe was about 7 feet wide, 6 feet 6 inches tall and 2 feet deep and weighed about a ton.
On the front of each bombe were places where rotors could be mounted. The rotors were in three groups of 12 triplets. Each triplet, arranged vertically, corresponded to the three Enigma rotors. The input and output of each triplet of rotors went to cable connectors, allowing the bombe to be rewired according to the Turing and Wlechman methodologies as applied to individual ciphertexts.
Using Polish codebreaking techniques, British cryptanalysts at Bletchley Park were, at the beginning of World War II, able to read Enigma messages by exploiting weaknesses in the German operating procedure. There was the concern that the Germans might at any point change their procedure rendering the current methods obsolete. To preempt this, British mathematician Alan Turing designed the bombe on a more general principle — the assumption of the presence of text that analysts could guess somewhere in the message, a cryptanalytical technique known as cribbing , also termed a known plaintext attack.
The first bombe, which was based on Turing's original design and so lacked a diagonal board, arrived at Bletchley Park in March and was named "Victory". The second bombe — "Agnus" — was equipped with Welchman's diagonal board, and was installed on 8 August ; bombes of this type were called "Spider" bombes. By the end of March , a more advanced version of the Bombe had been developed, the "Jumbo" machine. During , messages were broken on the two machines, nearly all successfully.
By the end of , there were 16 bombes in use. By the end of , this had increased to 49 bombes; at the end of , this figure had more than doubled to 99 bombes in operation. By May , there were operational machines, and required nearly 2, staff to operate. The Germans generally changed settings each day at midnight, the British goal was to find the new settings before the day was out, preferably by noon. With a motor spinning at RPM , all combinations would be tested in under 6 hours.
On average it would take half that time to find the correct match. After World War II, Winston Churchill ordered all the bombes destroyed, so no original material remains, although such an order appears to contradict the often-repeated story that use of Enigmas after the War was still encouraged, so the Allies could continue to read traffic from other countries.
As before, the unknown wiring would prevent the reading of the messages. Fortunately for the Allies, in December , before the machine went into official service, a submarine accidentally sent a message with four rotors, then sent the same message using only three, disclosing the wiring of the extra rotor.
In February the change became official and the ability to read the critical messages for the submarines largely ceased until new equipment became available which could use the information about the fourth rotor wiring to decrypt messages. That spring was known as the "Happy Time" for the submarines, with renewed success in their attacks on shipping due in part to the security of their communications and the German ability to read the convoy messages sent in Allied Naval Cipher No.
In May the US switched for the first time to using a convoy system and to requiring blackouts of coastal cities so ships wouldn't be silhouetted against their lights but the improvement was small. An urgent work plan to design bombes which could decrypt the four rotor system, with delivery scheduled for August or September of , was begun at Bletchley Park. In both diagrams the scramblers are at their correct positions. In order to minimise the risk of confusion the stecker partners of the letters on the menu are shown in lower case.
Diagram a shows the voltage path when the initial hypothesis is correct P is steckered to c , and the conclusion obtained confirms this. Note that the additional link through the diagonal board has had no effect on the outcome as it only joins together two points that are already on the same electrical path.
Diagram b shows the voltage path when a wrong initial hypothesis is used P is steckered to s , leading to the false conclusion: P is steckered to w.
In this case another link through the diagonal board generates a second false conclusion P steckered to n. The numerous additional links provided by the diagonal board usually generate large numbers of false conclusions from a false hypothesis, but do not compromise the true one.
In summary, the use of the diagonal board greatly increased the number of false conclusions derived from any false initial hypothesis so that it became possible to achieve simultaneous scanning with much less complex menus. In practice it was found very difficult to construct menus of this type from the wartime cribs that were available.
The condition required for the diagonal board to achieve the same effect was much less severe and simply consisted of a lower permissible limit for the number of letters on a menu, although the presence of one or more loops was still highly desirable. Essentially the Bombe is an electro-mechanical machine operating under the control of a complex system of electric relays. The duplicated wiring is needed in order to make the scramblers in the Bombe electrically symmetrical so that the currents in the individual wires of the menu circuit can pass through the scramblers in either direction.
The drums are mechanically connected to common drive shafts through a system of cams and gear wheels, and rotate at three different speeds. The prime mover is a 0. P DC electric motor. On the Bombe it is possible to set up a particular menu in triplicate with different sets of drums by making use of the three banks of locations available for them on the front of the machine. The drums are detachable and are colour coded to correspond to the five Enigma rotors they emulate; for example the drums coloured red, maroon and green correspond respectively to the Enigma rotors I, II and III.
The initial hypothesis is chosen by first selecting a suitable letter from the menu letter S in the example and then connecting the bank of twenty-six switches labelled A to Z that is mounted on the right-hand side of the machine, to a position on the menu circuit corresponding to this letter.
In the example this would be to wire A on the input to the scrambler at position S on the menu. Initially the three drums in each scrambler are turned by hand to the designated positions shown on the menu. Whenever the machine detects the necessary conditions i.
At Bletchley Park the first public demonstrations of the re-built bombe were made with a wartime menu derived from a crib for a weather forecast that had originally been used for the training of the WREN operators. This crib contains sixteen letter pairs as shown on the right. In this menu some of the information relating to the scrambler settings requires further explanation.
In the simple menu described previously the relative positions of the scramblers were represented by the corresponding positional numbers of the letter pairs as given in the crib. However in practice the Bombe operators set up these initial positions by means of circular reference scales of letters A — Z mounted on the faces of the drums, and the table on the right shows some examples of the way in which this was done.
For example position 2 on the menu would have the offset ZZB. The correct rotor order was already known to be:. The appropriate sets of drums were mounted on one of the three banks of positions available on the front of the machine. These special drums have circular reference scales on their faces similar to those on the other drums, but with the letters marked in the reverse order! This is the reason why the letters on the scales on the indicator drums are in the reverse order to those on all the other drums.
The information provided at the correct stop is as follows:. He produced the first detailed design of a stored-program computer, and became the foremost expert in artificial intelligence during his lifetime.
There can be few people more worthy than Turing. You can vote for who you think should appear on the new banknote here. Voting is open until December 14 th , and your nomination must be a scientist who is now deceased. Thanks for the detailed and clear essay on Turing and cracking the Enigma coding machine. Wright brothers, Helen Keller, etc.
Your email address will not be published. This site uses Akismet to reduce spam. Learn how your comment data is processed. Cracking stuff: how Turing beat the Enigma Departments Heritage Our partners 28th November More than 70 years after the Enigma was cracked by Alan Turing and his colleagues at Bletchley Park, innovative technology housed at The University of Manchester has provided a detailed peek beneath the bonnet of the German wartime cipher machine.
Leave a Reply Cancel reply Your email address will not be published. ScienceX: The eXtravaganza returns… greener than ever! North Campus: The weird and wonderful. Some keys would be broken within hours, some would never be broken — speed was always of the essence.
Prior to the war, in the s, three Polish mathematicians were the first to break the Enigma cipher. Using a Bomba machine in , they supplied valuable pre-war information from the simpler Enigma cipher techniques then being used. At Bletchley Park, attempts to decipher messages began. At the Park, Alan Turing was asked to find a way to break Enigma messages. Because of changes to the German operating procedures and the introduction of extra wheels, the Polish Bomba was now obsolete. This approach was aided by the fact that no letter on the Enigma could be represented by itself in an enciphered message.
Turing realised that his approach was capable of being mechanised, and his invention of the Bombe, together with Gordon Welchman's diagonal board, which dramatically reduced the number of invalid stops - false positives increased throughput to the point that the Bombe became a major success.
Throughout the war the operation built around Bombe machines and broke many keys on a daily basis. Huge amounts of intercepted traffic were deciphered, supplying invaluable information about enemy operations.
Many of the machines were located at out-stations, including Stanmore and Eastcote.
0コメント