In cryptography

Cryptography

Cryptography is the practice and study of techniques for secure communication in the presence of third parties...

, the clock was a method devised by Polish

Poland

Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...

 mathematician-cryptologist Jerzy Różycki

Jerzy Rózycki

Jerzy Witold Różycki was a Polish mathematician and cryptologist who worked at breaking German Enigma-machine ciphers.-Life:Różycki was born in what is now Ukraine, the fourth and youngest child of Zygmunt Różycki, a pharmacist and graduate of Saint Petersburg University, and Wanda, née Benita. ...

, at the Polish General Staff's Cipher Bureau

Biuro Szyfrów

The Biuro Szyfrów was the interwar Polish General Staff's agency charged with both cryptography and cryptology ....

, to facilitate decrypting German Enigma

Enigma machine

An Enigma machine is any of a family of related electro-mechanical rotor cipher machines used for the encryption and decryption of secret messages. Enigma was invented by German engineer Arthur Scherbius at the end of World War I...

 cipher

Cipher

In cryptography, a cipher is an algorithm for performing encryption or decryption — a series of well-defined steps that can be followed as a procedure. An alternative, less common term is encipherment. In non-technical usage, a “cipher” is the same thing as a “code”; however, the concepts...

s.

Method

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.

Różycki's "clock" method was later elaborated by the British cryptologist Alan Turing

Alan Turing

Alan Mathison Turing, OBE, FRS , was an English mathematician, logician, cryptanalyst, and computer scientist. He was highly influential in the development of computer science, providing a formalisation of the concepts of "algorithm" and "computation" with the Turing machine, which played a...

 at Bletchley Park

Bletchley Park

Bletchley Park is an estate located in the town of Bletchley, in Buckinghamshire, England, which currently houses the National Museum of Computing...

 in the development of a cryptological technique called "Banburismus

Banburismus

Banburismus was a cryptanalytic process developed by Alan Turing at Bletchley Park in England during the Second World War. It was used by Bletchley Park's Hut 8 to help break German Kriegsmarine messages enciphered on Enigma machines. The process used sequential conditional probability to infer...

."