How did Turing break enigma?
In: Technology
The structure and function of the Enigma cipher was mostly worked out by other intelligence operations exploiting operational errors and misuses by improperly trained German troops. When someone screwed up and transmitted the same thing twice but with different keys, or started transmitting the message in plaintext and then stopped, performed an encryption, and then transmitted again, this allowed Allied cryptanalysts to make deductions about how the Enigma worked structurally. Eventually, captured equipment helped them fill in all those gaps.
The thing was, knowing how it works structurally doesn’t necessarily mean you can decrypt the messages, you also need to know the key the messages were encrypted with, and that key was changed every day.
Turing worked out how, given a sufficient number of messages encrypted with the same key, to make some deductions about what that key must be – and critically, he designed an electromechanical device which could *perform* this very complicated calculation, which he called a bombe. From then on, cracking the codes was just a matter of running the bombes every day on that day’s intercepted messages, and letting them crank through the calculations until a key was found, and then everything could be read.
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