Hu Yoshida

ENIGMA: Cracking an Encryption Engine

Blog Post created by Hu Yoshida on Mar 13, 2015

On the way home from New York last week I saw the movie “Imitation Game”, which is the story of Alan Turing who led the effort to break the Enigma code with fellow mathematicians at Bletchley Park in the UK during World War II. Although, I rarely watch movies on long plane rides, I was fascinated by this movie, since I had just blogged about data encryption.


hu-031215.pngI am certainly not an expert on the subject of encryption or the history of Enigma, so most of what I am posting here comes from this movie and Wikipedia. Please send me comments if you find anything that is incorrect or would like to add any insights.


The Enigma machine was invented by the Germans after World War I, and was used commercially and by other countries to encrypt messages for many years. During World War II, an improved version was used by the German military. It had a series of stepping rotors, and plug boards which enabled a possible combination of 159 x 10^18 settings, which were changed on a daily basis. This is roughly equivalent to 2^60 in binary terms. In those days, using manual methods, it was nearly an impossible code to break, especially since the settings were changed daily. (The AES 256 that we use today has 2^256 possible combinations). In the movie the British had an Enigma machine which had been captured by the Poles, and although they could intercept the message at 6AM, which provided the settings for that day, it only gave them 18 hours to decipher the code before they had too start over again. To counter Enigma, Alan Turing built a machine to try to crack the code through brute force. At first, this was not fast enough to break through all the possible combinations. In the movie, one of the code ladies remarked that she could tell when a certain operator was sending messages due to his use of certain sequences of characters.  This helped to reduce the number of permutations that had to be processed and led to the cracking of the code. In the end it was operator mistakes, laziness and failure to systematically introduce changes in encryption procedures that cracked the code.  As is often the case, this result was due to people failure rather than a technology failure.


Alan Turing was a pioneering computer scientist, who is best known for his efforts to decipher the Enigma code. He is also known for the hypothetical device known as the Turing Machine, which can be adapted to simulate the logic of any computer algorithm. If you have a chance to visit, Silicon Valley, you should stop by the Computer History Museum in Mountain View where you can learn more about Alan Turing and see an actual Enigma machine on display. I also recommend seeing the Imitation Game movie, which is interesting in terms of how people can work together to solve problems. The title “Imitation Game” is not made very clear in the movie. Turing introduced the “Imitation Game” in a paper he wrote to pose the question whether a computer could “imitate” a man.


The title was less relevant to the computer that broke the enigma code than to the breaking of the man.