# How to deduce enigma settings given a partial plaintext?

Assuming some large block of text is encrypted with an enigma machine and I only know a small subset of letters before and after encryption, how do I go about figuring out the enigma settings from this point?

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Nice try, time traveling Alan Turing. –  Ethan Heilman Oct 28 '11 at 14:43
The first result I get when I search Google for "enigma cryptanalysis" is the Wikipedia article on Cryptanalysis of the Enigma. Do you have some specific question which it (or the other search results on the first page) don't answer? –  Ilmari Karonen Oct 28 '11 at 20:30

According to "Applied Cryptanalysis", the theoretical keyspace of Enigma is approximately $2^{366}$, but due to practical limitations, Enigma as used by the Germans only had a keyspace of approximately $2^{77}$. Given the power of some of the clouds out there (with GPUs and all), I bet you could do a brute-force attack of the 77-bit key space in a reasonable amount of time. Deep Crack could brute-force the 56-bit key space of DES in about 4.5 days. I'd think we could do much better than that today.
@EthanHeilman, I hadn't plugged the number when I wrote my answer, so I wasn't completely sure. I did just run the numbers, however, and got 265 years. For my math, I did 4.5 days is s=388,800 seconds. So I took $ops = 2^{56}/s$ to get operations per second. I then did $2^{77}/(ops*100)$ to get the number of seconds for $2^{77}$ operations and assuming a machine 100 times faster. I then converted the answer to years. Am I doing something wrong? –  mikeazo Nov 1 '11 at 21:54