![]() However, the rings have notches in them (either one or two in the original Enigma machines), and when the pawl is positioned over a notch in the ring for the rotor to its right, it slips through to its own rotor and pushes it forward. ![]() ring usually holds the pawl away from its own ratchet, preventing the rotor wheel to its left from moving. Here is a good visualization of how signals travel through the rotors and how messages are encrypted. The pawls pushing the other rotors, however, are normally blocked from engaging their rotors by the alphabet ring on the left side of the rotor to their right. The lever on the rightmost rotor ( N) always succeeds, so that rotor N (the “fast” rotor) rotates one position before each character. Thus, pawls always try to engage with the ratchet of their own rotor. Before a letter of a message is translated, a spring-loaded pawl (lever)-one to the right of each rotating rotor-tries to engage the ratchet on the right side of its rotor and thus rotate its rotor by one position, changing the permutation performed by the rotor. Each rotor has a circular ratchet on its right side and an “alphabet ring” on its left side that fits over the ratchet of the rotor to its left. The overall permutation changes with each successive letter because some rotors rotate after encrypting a letter. ![]() In actual Enigma machines, it was fixed for any given model (the Kreigsmarine (Navy) used N = 5 (four rotors and reflector) and the Wehrmacht used N = 4.) In our simulator, N will be a configuration parameter. In what follows, we’ll refer to the selected reflector and rotors in a machine’s configuration as 1 through N, with 1 being the reflector, and N the rightmost rotor. The reflector’s permutation was designed to be a derangement, so each letter was mapped to a different letter, which guaranteed that the letter inputted into the enigma machine would be different than the one outputted. This configuration is the first part of the secret key used to encrypt or decrypt a message. But it does a great deal of good to be able to eliminate possible decryptions because some of their letters are the same as in the plaintext.)Įach rotor and each reflector implements a different permutation, and the overall effect depends on their configuration: which rotors and reflector are used, what order they are placed in the machine, and which rotational position they are initially set to. It doesn’t really do a would-be code-breaker any good to know that some letters in an encrypted message might be the same as those in the plaintext if he doesn’t know which ones. (This was a significant cryptographic weakness, as it turned out. A signal starting from the rightmost rotor enters through one of the 26 possible contacts, flows through wires in the rotors, “bounces” off the reflector, and then comes back through the same rotors (in reverse) by a different route, always ending up being permuted to a letter position different from where it started that is, the permutation was always a derangement. To the left of the rotors, one could select one of a set of reflectors ( Umkehrwalzen), with contacts on their right sides only, and wired to connect half of those contacts to the other half. Most of these rotors have 26 contacts on both sides, which are wired together internally to effect a permutation of signals coming in from one side onto the contacts on the other (and the inverse permutation when going in the reverse direction). ![]() The device consists of a simple mechanical system of (partially) interchangeable rotors ( Walzen) that sit side-by-side on a shaft and make electrical contact with each other. This made decryption considerably more difficult. The Enigma, however, implements a progressive substitution, different for each subsequent letter of the message. The alphabet consists solely of the 26 letters in one case (there were various conventions for spaces and punctuation).īut Plain substitution ciphers are easy to break. That is, at any given time, the machine performs a permutation-a one-to-one mapping-of the alphabet onto itself. The Enigmas effect a substitution cipher on the letters of a message. Shows one version of the machine looked like and how it operated ![]()
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