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"Heil Hitler"....how can these two words help in breaking the most sophisticated machine of that time in The Imitation Game (2014)?

Glorfindel
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INVICTUS XOXO
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    Numberphile has a great two-part video series on this topic: 1.) https://www.youtube.com/watch?v=G2_Q9FoD-oQ 2.) https://youtu.be/V4V2bpZlqx8 – Lil' Bits Mar 11 '19 at 18:48
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    For the record, the movie is wildly inaccurate on practically the entire story. He didn't invent that machine, there was far more than one of them, everybody knew about cribs and they were already using them and didn't need some bar floozy to teach them about it, he wasn't intellectually crippled by his chemical castration, etc. I did like the movie, but it's more fiction than non-fiction. – zibadawa timmy Mar 11 '19 at 21:00
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    You can find a detailed explanation of how Turing's machine worked here. – DarthFennec Mar 11 '19 at 23:53
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    He also not anywhere near as socially awkward as depicted, as he had enough social ability to conduct numerous same-sex affairs while that was illegal and could have been career-ending blackmail material for someone with access to highly classified material. But "socially awkward genius" is now a trope, and one that Cumberbatch has built his career on, so... – Ross Thompson Mar 13 '19 at 15:13
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    Agreed with @zibadawatimmy - this film is not one to watch for historical accuracy. Almost everything in it is wrong. The 'heil hitler' crib wasn't even useful in breaking the navy enigma, which is what Turing's team in Hut 8 were almost exclusively working on. The film also depicts the breaking of Enigma as a thing that happened at a single point in time, before which it was not read and after which it was - this is also completely wrong. Enigma was being read throughout the war - what changed was how quickly it could be decoded and how quickly the British could react to changes in the code. – J... Mar 13 '19 at 18:07
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    If anyone is looking for a good book on the topic, Enigma: The Battle for the Code by Hugh Sebag-Montefiore is an excellent review. – J... Mar 13 '19 at 18:09

1 Answers1

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The actual decryption was very complex but Bletchley Park was given a BIG clue because...

To aid this process, all Turing needed was a word (or a group of words) that he was positive the Germans would use in each of their Enigma-encrypted messages. What was that word, or rather, that phrase?

‘Heil Hitler’

Germans put the phrase ‘Heil Hitler’ at the end of every encrypted message. This seemingly small mistake eventually contributed to their ultimate defeat.

Read more at the Source

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Paulie_D
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    Another example - the allies knew the first message of the day was usually a weather report, and they knew what the weather was, so could look for matches of e.g. "Regen" or "17 Grad Celsius" in those in order to get the key for the day. – OrangeDog Mar 11 '19 at 17:28
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    It's called "crib". Another reliable crib was word "eins" (one), so the cryptographers created so called "eins catalogue", similar to today rainbow tables ;-) – Edheldil Mar 11 '19 at 17:49
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    The limitation that allowed the Allies to break the Enigma was that any letter on the Enigma keyboard typed would never result in that letter as being an output. You could never press 'a' and get 'a'. This, and knowledge of the contents (usually called a "known plaintext attack"), allowed the Allies to brute force attack ciphertexts. – Naftuli Kay Mar 11 '19 at 18:47
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    @NaftuliKay that seems more like a complete answer than a comment – Aethenosity Mar 12 '19 at 01:24
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    Also heard that one German, supposedly in a quite outpost, send something like: "I have nothing to report" everyday which helped break the enigma code. – user2121 Mar 12 '19 at 11:32
  • While 'Heil Hitler' was a common crib, I don't think it was appended to the end of every message. I've read several books on Bletchley Park, and none of them said anything like that. If a single phrase were present in every message, decoding would have been trivial. – Hobbes Mar 12 '19 at 13:43
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    @Hobbes, this answer is referring to events in the movie, not in real life. – Doctor Jones Mar 12 '19 at 14:43
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    @Hobbes Maybe not every message, but enough that they could find the pattern. – Barmar Mar 12 '19 at 20:04
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    IIRC, another interesting crib came about when a (bored) German operator was asked to send a test message. When the cryptanalyst in Bletchley Park got the message, she (IIRC) was surprised to see there was not a single letter "L" in the entire text..... sure enough the operator had simply repeatedly pressed "L". I believe another operator had a habit of using the same first three letters of his girlfriend's name, CIL, as the "session key". These were known at BP as "cillies" https://www.cryptomuseum.com/crypto/enigma/glossary.htm – Simon F Mar 13 '19 at 09:54
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    Another trick BP used was that of "gardening" where they'd ask the RAF to drop some mines in a known location (aka seeding) and then look for the German message reporting it. https://aldrichames.wordpress.com/page/8/ – Simon F Mar 13 '19 at 10:17
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    @SimonF There were two three letter keys (plugboard settings, and wheel settings). It wasn't unusual for operators to choose obvious settings like BER-LIN or LON-DON, which were fairly quick to check before making a more comprehensive attack. – Ross Thompson Mar 13 '19 at 15:17
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    @RossThompson But weren't those pre-determined by a big book of settings (along with choice of rotors)? Once those were set up for the day, the operator then was meant, on a per message basis, to "randomly" type 3 letters, then reset the 3 rotors to those letters. The receiver, at the other end, would decode the first three letters, and then adjust the rotors to those transmitted settings and then decode the remainder of the message. (FWIW the Polish decryption attack early in the war/prewar(?) used the fact the Germans originally encoded those 3 characters twice, which was security flaw) – Simon F Mar 13 '19 at 16:18
  • Yeah, it's been a while... IIRC, if the day's plugboard settings were BER, then operators would use LIN for the wheel settings? – Ross Thompson Mar 13 '19 at 20:24
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    @NaftuliKay That was hardly the only tool used at BP for breaking Enigma. It was one single weakness, among many that were exploited. Enigma was broken out of a combination of previous work by Polish cryptographers, the Navy's ongoing efforts to capture Enigma codebooks, bigram tables, etc, the design of Turing's new bombe machines, a long list of heuristic approaches, numerous procedural deficiencies used by the Germans, the development of the Banburismus method, gardening for cribs, etc. It was a wildly complex endeavour - you can't say it was because of a single thing like that. – J... Mar 14 '19 at 11:45
  • @RossThompson Hmm but having just watched the "numberphile" video ( youtube.com/watch?v=G2_Q9FoD-oQ) from the first comment on the OP, I'm a bit puzzled. I thought the windows on the rotors displayed a letter position so that a message key could be communicated. These only seem to show numbers. – Simon F Mar 14 '19 at 14:28
  • @RossThompson What a strange coincidence. Just saw a picture on twitter (https://pbs.twimg.com/media/D1qADsWUkAA2kDL.jpg) of the notice inside the lid, and it shows the mapping from rotor position to alphabet. That fixes my confusion on how the new rotor positions were communicated at the start of each message. – Simon F Mar 15 '19 at 09:06