Grill (cryptology)

The grill ( _pl. ruszt), in cryptology, was a method used, chiefly early on, by the mathematician-cryptologists of the Polish Cipher Bureau in decrypting German Enigma machine ciphers.

The grill method was described by Marian Rejewski as being "manual and tedious" and, like the later cryptologic bomb, as being "based... on the fact that the plug connections [in the Enigma's commutator, or "plugboard"] did not change all the letters." Unlike the bomb, however, "the grill method required unchanged "pairs" of letters [rather than] only unchanged letters."

The grill method found application as late as December 1938 in working out the wiring in two Enigma rotors newly introduced by the Germans. (This was made possible by the fact that a "Sicherheitsdienst" net, while it had introduced the new drums IV and V, continued using the old system for enciphering the individual message keys.)

References

* Władysław Kozaczuk, "Enigma: How the German Machine Cipher Was Broken, and How It Was Read by the Allies in World War Two", edited and translated by Christopher Kasparek, Frederick, MD, University Publications of America, 1984, pp. 242, 268, 290.