![]() Thanks to the reflector, decoding was the same as encoding the text, but in reverse.īut that reflector also led to the flaw in Enigma, and the basis on which all codebreaking efforts were founded: no letter would ever be encoded as itself. From there, decoding is as simple as typing the cyphertext back into the machine. In the earliest machines, up to six pairs could be swapped in that way later models pushed it to 10, and added a fourth rotor.ĭespite the complexity, all the operators needed was information about the starting position, and order, of the three rotors, plus the positions of the plugs in the board. Adding to the scrambling was a plugboard, sitting between the main rotors and the input and output, which swapped pairs of letters. When the first rotor has turned through all 26 positions, the second rotor clicks round, and when that’s made it round all the way, the third does the same, leading to more than 17,000 different combinations before the encryption process repeats itself. The board lights up to show the encrypted output, and the first of the three rotors clicks round one position – changing the output even if the second letter input is the same as the first one. ![]() That letter passes through all three rotors, bounces off a “reflector” at the end, and passes back through all three rotors in the other direction. Each takes in a letter and outputs it as a different one. Inside the box, the system is built around three physical rotors.
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