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As you can probably guess, I just watched The Imitation Game, which hasn't really gotten points for historical accuracy...

During World War II, Turing and his team fret that they can't know the plaintext of the Enigma messages they intercept. In a Eureka moment, it occurs to Turing to try a message that probably contains the words "Heil Hitler."

My question is then: Hadn't it occurred to anyone in the past, say, during the Civil War or World War I, to try something like this to break a code? (I might be mixing up known plaintext and chosen plaintext attacks, please let me know).

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  • $\begingroup$ In times of the Enigma, people were still convinced of "if I can't think of an attack, then it is secure". Security by obscurity was also still a "valid" point of view for the people. (Kerckhoff was earlier, but there's a difference between science and practice - it still is) Much has changed after WW2. $\endgroup$ – tylo Feb 10 '15 at 10:30
  • $\begingroup$ Cribs are indeed a subset of known-plaintext attack. Chosen-plaintext attacks were also used (you couldn't choose the whole plaintext, but you could do something that you knew they'd report and intercept the report). $\endgroup$ – cpast Feb 10 '15 at 17:10
  • $\begingroup$ The real question is "How his machine is even supposed to stop if they have no idea about the plaintext?". It's just trying every combination without any way to check if the result is valid.. $\endgroup$ – Dillinur Feb 11 '15 at 10:02
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No, the idea is much older. Don't trust the movie too far, Turing actually searched for the word "eins" (one) because it was the most common number used. Far more likely to appear than "Heil Hitler" but it doesn't make good screen drama.

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