# 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?

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