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The Technology Behind ‘The Imitation Game’

By Rosalyn Brady

February 24, 2023

UPDATED 12:00 PM EST


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[Photo Credit: The Imitation Game Official Trailer #1]

Morten Tyldum’s 2014 film The Imitation Game is a biopic of cryptanalyst and mathematician Alan Turing, who played a crucial role in deciphering the Enigma Code used by the German army to send encrypted messages during the Second World War. The Enigma Code was generated by Enigma machines, cipher machines that could translate messages in and out of code. Enigma machines do this using several sets of rotating wheels (rotors) and a plugboard that conducts the electric signal from the standard alphabet to the coded one. When a key on an Enigma machine’s keyboard is pressed, it sends an electric signal to the plugboard, which has a point of contact for each letter of the alphabet on either side of it. The first set of contact points is in standard alphabetical order, while the second is in code. The signal then passes through a static rotor, which acts as a point of contact between the plugboard and rotors.


There are typically between three and eight rotors. Each has a key for each letter of the alphabet, and notches that sometimes move the next rotor as well. When the signal reaches it, the first rotor rotates by one key to change the code. For example, if B on the first rotor was connected to D on the next rotor, and someone pressed B on the keyboard, that first rotor would move and C would be connected to D. When a rotor makes a full revolution, its notch will push the next rotor forward - in this case, B and C would be connected to E on their next revolution. The electric signal passes through each rotor and is then reflected back to the static wheel and the plugboard, and the letter to be used in the code, which is the letter displayed on the last rotor, lights up on a lampboard. Since each of the 26 letters have 26 routes to take through each of the three rotors, there are 17,576 possible code combinations.


Due to the Enigma machine’s efficacy, it was used by the Germans to send encrypted messages regarding army, navy, Air Force, and diplomatic operations such as battle plans, reports, and invasions during the Second World War. An integral part of the Allied victory was breaking this Enigma Code, which was done by Alan Turing and his team at Bletchley Park. It is this story that The Imitation Game tells.


Turing developed a machine called the Bombe to decipher messages. The Bombe worked much like the Enigma machine, with the same plugboard, rotors, and contact points for each letter of the alphabet, and it used this technology to sift through the myriad possible code combinations and decode Enigma messages. However, it was human logic that accelerated these breakthroughs. Turing discovered that no letter would be encrypted as itself, and this decreased the number of code combinations exponentially and made it much easier to decrypt Enigma messages now that his team knew of this flaw in the Enigma Code. Additionally, the team was able to make educated guesses at words each message would contain, such as ‘eins’, the German word for ‘one’, ‘Wetter’, the German word for weather, or an outdated German sign-off that was then common. By 1943, 84,000 Enigma messages were being decoded monthly - or two every minute.


It was this that allowed Turing and his team to break the Enigma Code and gain the information that helped secure an Allied victory, and it is the story of this feat, and the technology involved, that The Imitation Game relays.



References


Copeland, Jack. “Alan Turing: The Codebreaker Who Saved ‘millions of Lives.’” BBC News, 19 June 2012, www.bbc.com/news/technology-18419691.



“Enigma Encoding Machine.” National Museums Scotland, www.nms.ac.uk/explore-our-collections/stories/science-and-technology/enigma-encoding-machine.



Dufresne, Steven. “The Enigma Enigma: How the Enigma Machine Worked.” Hackaday, 22 Aug. 2017, hackaday.com/2017/08/22/the-enigma-enigma-how-the-enigma-machine-worked.



A., Ashish. “Cracking the Uncrackable: How Did Alan Turing and His Team Crack the Enigma Code?” Science ABC, 8 July 2022, www.scienceabc.com/innovation/cracking-the-uncrackable-how-did-alan-turing-and-his-team-crack-the-enigma-code.html.



“History of WW2: How Bletchley Park Cracked the Enigma Code.” Sky HISTORY TV Channel, www.history.co.uk/history-of-ww2/code-breaking.



H., Hayley. “Cracking Stuff: How Turing Beat the Enigma.” University of Manchester, 28 Nov. 2018.



Carter, Frank. “The Turing Bombe in Bletchley Park.” Rutherford Journal, rutherfordjournal.org/article030108.html.











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