Clock (cryptography)

In cryptography, the clock was a method devised by Polish mathematician-cryptologist Jerzy Różycki, at the Polish General Staff's Cipher Bureau, to facilitate decrypting German Enigma ciphers.

The method determined the rightmost rotor in the German Enigma by exploiting the different turnover positions. For the Poles, learning the rightmost rotor reduced the rotor-order search space by a factor of 3 (the number of rotors).

The British subsequently improved the method, allowing them to use their limited number of bombes more effectively (the British confronted 5 to 8 rotors).