Eli5 how did the allies in ww2 decipher German enigma if there were millions of possibilities for letters and it was being changed every day?
In: 14
They did it in a few ways. The first breakthrough was by looking for words they knew were likely to be there. Every morning the German military sent out a weather report. The codebreakers knew that the report was almost certain to contain the German word for weather, “wetter,” and that almost all messages contained the the phrase “heil Hitler.” This meant that, at a minimum, the weather report gave them the letters W, E, T, R, H, I, and L.
Once that was figured out there were able to look at past messages and find out two other major things:
The first is that a letter was never encoded as itself, the first letter in “wetter” would never be “W.” That eliminated one possibility for each letter, and going from 26 possibilities to 25 makes a huge difference.
The second is that numbers were always spelled out, it was “eins” rather than “1.” So if there were numbers involved, which there frequently were, you got those letters as well. So just from “wetter,” “heil Hitler,” and the numbers 0 to 12 you would have the letters W, E, T, R, H, I, L, N, U, S, Z, D, V, F, C, B, A, and O. That’s more than half the alphabet and every single vowel.
At that point it’s sort of like Wheel of Fortune because letters aren’t in random orders, they’re spelling out words and those words have context. For example “— — —– —-” could be anything, but once I have filled in “one two t_ree fo_r” it becomes obvious what the missing letters are.
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