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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).
This method sometimes made it possible to determine which of the Enigma machine's rotors was at the far right, that is, in the position where the rotor always revolved at every depression of a key. The clock method was developed by Jerzy Różycki during 1933–1935.
Marian Rejewski's grill method could determine the right-hand rotor, but that involved trying each possible rotor permutation (there were three rotors at the time) at each of its 26 possible starting rotations. The grill method tests were also complicated by the plugboard settings. In contrast, the clock method involved simple tests that were unaffected by the plugboard.
In the early 1930s, determining the rotor order was not a significant burden because the Germans used the same rotor order for three months at a time. The rotor order could be determined once, and then that order could be used for the next three months. On 1 February 1936, the Germans changed the rotor order every month. On 1 November 1936, the Germans changed the rotor order every day.
Różycki's "clock" method was later elaborated by the British cryptologist Alan Turing at Bletchley Park in the development of a cryptological technique called "Banburismus."
The Cipher Bureau received German radio intercepts enciphered by the Enigma machine. With about 60 messages, the Bureau could determine Marian Rejewski's characteristic structure for the message key encoding. By exploiting poor message keys, the Bureau could determine the message key encoding. At that point, the cryptanalysts may know only the message keys and their ciphertext. They may not know the other secrets of the daily key such as the plugboard setting, the ring settings, the rotor order, or the initial setting. With such little information and some luck, the Poles could still determine which rotor was the rightmost.
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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).
This method sometimes made it possible to determine which of the Enigma machine's rotors was at the far right, that is, in the position where the rotor always revolved at every depression of a key. The clock method was developed by Jerzy Różycki during 1933–1935.
Marian Rejewski's grill method could determine the right-hand rotor, but that involved trying each possible rotor permutation (there were three rotors at the time) at each of its 26 possible starting rotations. The grill method tests were also complicated by the plugboard settings. In contrast, the clock method involved simple tests that were unaffected by the plugboard.
In the early 1930s, determining the rotor order was not a significant burden because the Germans used the same rotor order for three months at a time. The rotor order could be determined once, and then that order could be used for the next three months. On 1 February 1936, the Germans changed the rotor order every month. On 1 November 1936, the Germans changed the rotor order every day.
Różycki's "clock" method was later elaborated by the British cryptologist Alan Turing at Bletchley Park in the development of a cryptological technique called "Banburismus."
The Cipher Bureau received German radio intercepts enciphered by the Enigma machine. With about 60 messages, the Bureau could determine Marian Rejewski's characteristic structure for the message key encoding. By exploiting poor message keys, the Bureau could determine the message key encoding. At that point, the cryptanalysts may know only the message keys and their ciphertext. They may not know the other secrets of the daily key such as the plugboard setting, the ring settings, the rotor order, or the initial setting. With such little information and some luck, the Poles could still determine which rotor was the rightmost.