The History Column: The Polish Cryptographers Marian Rejewski, Jerzy Różycki and Henryk Zygalski
Marian Rejewski, Jerzy Różycki and Henryk Zygalski were Polish mathematicians / cryptographers who worked for the Polish General Staff's Cipher Bureau in the 1930s. They made key contributions to the understanding of the German Enigma machine, paving the way for the codebreaking work at Bletchley Park in the UK in WW2.
The Enigma machine was invented and patented in Germany in 1918 by an engineer named Arthur Scherbius. In the picture opposite it can be seen that the machine consists of a keyboard, a plugboard (at the front), a set of three rotors, each with 26 letters around the rim, and (at the top) a set of indicator lamps, one for each letter of the alphabet. There were no numbers, so these had to be spelled out individually.
The key part of the design is the three rotors. All Enigma sets were provided with the same set of five rotors, and periodically-issued instructions (codebook) as to which three rotors should be used and in which order, and which plugboard settings, extending for a number of weeks. When a key was pressed, the selected letter passed via the plugboard to the first rotor, which mapped it to another letter, thence to the second rotor, and thence to the third rotor, then back again, illuminating the encrypted letter on the set of indicator lamps, which was noted by hand. When the next key was pressed, the first rotor rotated by one increment. When the first rotor had completed one complete revolution, the second rotor rotated by one increment, and so on. A consequence of this is that no letter could map to itself. In this way the mapping of the encryption changed with each symbol, and led to the presumption that it was unbreakable – but that was far from the case. To establish communication with another Enigma station it was necessary to synchronise the initial positions of the rotors of the two machines, and this required encrypting and sending a message composed of three letters chosen by the operator, twice in succession. This procedure represented a weakness, since operators might choose easily-guessed combinations such as girlfriends’ names or rude words. The encrypted message was then transmitted by Morse code in five-letter groups, then decrypted by the Enigma machine at the receive station.
Enigma was used extensively by German forces prior to and during WW2, especially for communications where landline would not be possible – such as with ships or U-boats, or with fast-moving army units. Various refinements and improvements were made throughout WW2, and there were perhaps as many as 100 different codes, by no means all of which were broken.
In 1932 a spy, Hans-Thilo Schmidt, had managed to obtain information on Enigma, including the daily keys used for September and October 1932, and this information was passed to France and to Poland. Rejewski, Różycki and Zygalski were able to use this information, together with Enigma traffic at that time, to deduce the structure of the machine, including the rotor wirings, despite never having seen one at first hand. Furthermore, they were able to understand some of the weaknesses of the machine and to determine how these might be exploited, including so-called Zygalski sheets and the bomba (bombe), which was a device to search for rotor settings.
In September 1939, as the situation in Europe deteriorated, Rejewski, Różycki and Zygalski fled to France, and then to North Africa. Różycki died when the ship on which he was travelling sank, but Rejewski and Zygalski managed to reach Britain.
The British codebreaking activity at Bletchley Park was judged to be so secret that it could not be revealed to them. Nevertheless, the work and insight of all three was fundamental to the work of Bletchley Park. One of the principal codebreakers, Gordon Welchman, wrote: ‘Hut 6 Ultra [the name used for they intelligence gained from Enigma] would never have got off the ground if we had not learned from the Poles, in the nick of time, the details both of the German military version of the commercial Enigma machine, and of the operating procedures that were in use’.
After the War Rejewski and Zygalski returned to Poland, and all three were honoured by their country: there is a monument to them at Poznań University, and Rejewski and Zygalski were posthumously awarded Poland's second-highest civilian decoration, the Grand Cross of the Order of Polonia Restituta. In 2014 their work was recognised as an IEEE Historic Milestone.
Acknowledgement: I express my thanks to Phil Judkins, and to Mateusz Malanowski, Piotr Samczynski, and Krzysztof Kulpa for their help and advice. Further information may be found in:
- Carter, Frank, The First Breaking of Enigma: Some of the Pioneering Techniques Developed by the Polish Cipher Bureau, Report No 2, Bletchley Park Trust, 2008.
- Sebag-Montefiore, Hugh, Enigma: The Battle For The Code, Weidenfeld & Nicolson, 2001.
Authored by Hugh D. Griffiths
University College London