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| September 11, 2001 »
September 12, 2006
Turing Bombe Recreated at Bletchley Park
Posted on September 12, 2006 at 2:40 PM
• 20 Comments
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The article says the bombe "tried out all the possible combinations in which the German encoding machine Enigma could be set". I'm fairly sure that is not correct. I think the mathematical work done by Alan Turing and others was used to eliminate most of the possible combinations and try the relatively small number remaining. A brute force attack, even if mechanized, would have been too slow.
Hope they have one of the Enigmas (or Enigma replicas) on hand as well.
@C. N. Cary
It would have been more technically correct to say that "it was capable of trying all of the combinations to which a 3-rotor Enigma could be configured" (somewhat inexact quote of a recent documentary of the work of a previously classified group of cryptographers, machinists, and engineers at an NCR facility in Ohio during the latter part of the war on a 4-rotor bombe style machine).
It is probably also worth noting at this point that "bombe" isn't meant to be pronounced "bomb" and should not be confused with the latter. The actual origin of the word "bombe" was made note of in the aforementioned documentary, and if memory serves it was the name given the device by the man whom came up with the theoretical design for it. The word was from his native language is was from some derivative of Czech or Polish if memory serves correctly. I believe that the final "e" is actually supposed to be "è" or "é" or something of the like.
aikimark: The last time I went to Bletchley, they did have a replica three-rotor Enigma which you could use to encode a message, along with a software-simulated Bombe which you could use to break it.
For those interested here is a link to an article about it at the present day Bletchley Park National Codes Centre; not sure on the sites policy with regards to posting links so prefix with www.
and if your interested in a virtual Enigma machine see the CD in the shop section.
The Bombe was used to brute force the initial settings of the rotors. There's also a plugboard, but the plugboard couldn't be, and still can't be brute forced, but the WWII cryptographers had worked out a way around the plugboard in some common situations. When one of these situations occured, the bombe would decrypt the message in a few hours.
The other messages which didn't have the plugboard in a decryptable state, it's humbling to realise that many of these messages have still not been decrypted, 60 years later, and probably still can't be with the best techniques known.
Whatever you do, don't discuss this arcticle on an airplane. And don't read about it, either. No one is going to know the "bombe" isn't an explosive device, and you may suffer the consequences of their misunderstanding.
@C. N. Cary
Yeah i also think you are right, there are too many combinations with 6 wheels or dials.
If I remember correctly the Bombe was based on "Bomba kryptologiczna", "Cryptologic bomb" that was created in Poland and sent over to England when it was clear that Poland was about to surrender. Turing did a lot of work, but it's a little impolite not to give the polish cryptographers some credit.
But it seems like people often forget anything not done by the Germans or the Allies during the war. Personally I consider the attack on Geheimschreiber that was made by Arne Beurling far more impressive...
Apolgies there. Please use the links from the first of the above 2 comments; the second comment has an error from an extra full stop being included in the link address.
It's a shame that the artical did not mention that the only reason Bletchley Park is avaialble as a museum was due to the very very hard work of pretty much one man Tony Sale. He became the museums first director from 1993 to 1999.
He managed to convince Milton Keynes Local Council that what they had was a very unique and irreplasable piece of history.
Sadly other sites such as Pounden, Gawcott etc have gone the way of the "Business Park". Most of MI6's/F&CO stuff moved to Hanslope Park.
You can see more on Bletchly on Tony's own site,
I still wondering how they found out about the wiring of the enigma machine used by the germans, i cannot find any information about this. Because if you do not know how the rotors are wired the task of decryption is almost impossible. So they must had have a few clues of how the rotors we're wired. Anyone info on this?
Ah this provides some useful insight:
Alan Turing realized that the solution did not lie in creating a machine that replicated sixty Enigmas. The Polish Bomba searched for matches in indicators. Once already the Germans had changed how indicators were used, throwing the Poles back into the darkness until new Zygalski sheets could be cut. The Germans could easily change the indicators again. Turing began thinking about a machine that worked, not with the indicators, but with assumed text. By using text that cryptanalysts assumed appeared in the message, the machine would not be dependent on the indicators.
Like the Polish Bomba, the machine Turing conceived would also run through all the possible settings. Rotors and wires would simulate a series of Enigma rotors and pass an electrical current from one rotor to the next. However, rather than looking for the one correct rotor setting based on the indicators, as the Bomba did, Turing’s would look for all the rotor settings that allowed the cipher to match the assumed plain text. Or, more correctly, it searched all the settings and disregarded those that were incorrect.
For example, if the assumed letter was "G" and the corresponding cipher letter was "L," Turing’s test register ignored any results that did not allow the electrical current to pass from "G" to "L." By__disproving__thousands of rotor settings, those left were possible correct settings.
So this reminds me about edison who said something like: "i found a million ways how not to make a lightbulb."
I have not dived into the Turing story much but, this isn't very analytical if i may say so., but a mere trial and error approach.
Look up Marian Rejewski and other Polish Cryptographers on the web. I think what happened was the germans would transmit their 3 letter rotor starting positions twice e.g. PQX PQX at the start of the message. So the cryptographers would know that the first and fourth letters would be the same etc. With many messages they were able to figure out the wiring. The Germans stopped doing this after a while.
Later, Enigma machines were captured, of course.
I do believe what was explianed in the documentary about the American follow-up to the Bletchley Park work was that often, against orders, German officers would send things like their own initials and their girlfriend's initials at the beginning of EVERY message that they sent as their "init string" instead of using six random letters at the beginning of the message (and one could tell by radiolocation and a little wit which operator was sending the message--every "fist" sounds different). This sort of thing was supposed to be done to throw off attempts by Allied cryptographers to decrypt messages in the case that the Allies captured the wheel setting schedules. Obviously, once said sequences were discovered the pace of decryption accelerated dramatically--until the introduction of the four-rotor enigma.
I just remembered the name of said documentary. More can be found at:
"Later, Enigma machines were captured, of course."
Actually, a little-known fact is that the Poles intercepted an Enigma machine prior to the outbreak of hostilities. It was sent to a German company in Poland, and when the German embassy found out it was being detained in customs, they raised a fuss, came up with some story about a mistkae, and this apparently piqued the Pole's interest enough that their security service got wind of it and managed to get all the relevant details and photos of the equipment before turning it back over.
I can dig up the link if time permits.
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