Grill (cryptology)

The grill method (metoda rusztu), in cryptology, was a method used chiefly early on, before the advent of the cyclometer, by the mathematician-cryptologists of the Polish Cipher Bureau (Biuro Szyfrów) in decrypting German Enigma machine ciphers. The Enigma rotor cipher machine changes plaintext characters into cipher text using a different permutation for each character, and so implements a polyalphabetic substitution cipher. The German navy started using Enigma machines in 1926; it was called Funkschlüssel C ("Radio cipher C"). By 15 July 1928, the German Army (Reichswehr) had introduced their own version of the Enigma—the Enigma G; a revised Enigma I (with plugboard) appeared in June 1930. The Enigma I used by the German military in the 1930s was a 3-rotor machine. Initially, there were only three rotors labeled I, II, and III, but they could be arranged in any order when placed in the machine. Rejewski identified the rotor permutations by L, M, and N; the encipherment produced by the rotors altered as each character was encrypted. The rightmost permutation (N) changed with each character. In addition, there was a plugboard that did some additional scrambling. The number of possible different rotor wirings is: The number of possible different reflector wirings is: A perhaps more intuitive way of arriving at this figure is to consider that 1 letter can be wired to any of 25. That leaves 24 letters to connect. The next chosen letter can connect to any of 23. And so on. The number of possible different plugboard wirings (for six cables) is: To encrypt or decrypt, the operator made the following machine key settings: the rotor order (Walzenlage) the ring settings (Ringstellung) the plugboard connections (Steckerverbindung) an initial rotor position (Grundstellung) In the early 1930s, the Germans distributed a secret monthly list of all the daily machine settings. The Germans knew that it would be foolish to encrypt the day's traffic using the same key, so each message had its own "message key".