Enigma Machine

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Germany’s Enigma is an electro-mechanical cipher machine that uses a series of rotating wheels and ever-changing electrical pathways to turn plain text into a scrambled message.  Most notably used by the Nazi military during WWII, German authorities considered the code system unbreakable and used Enigma to transmit some of their most secret messages.
Their confidence in the machine was well-founded.  Enigma could generate billions of letter combinations, each different from the last.  As a letter was typed into the keyboard, one or more of the rotors moved, changing the electrical pathway through the machine.  Additional complexity could be achieved through varying the order of the rotors, the initial settings of each rotor, and through 26 pairs of output-switching sockets located on the front face of the machine.  Without a codebook to reveal the proper plug and rotor settings, there were more than 107,000,000,000,000,000,000 possibilities.  And even if a code was broken by some stroke of luck, the settings for Enigma were changed every day.
The machine did not send or receive communications; it simply scrambled messages into blocks of seemingly undecipherable text.  When a key was depressed by the operator, a single letter would illuminate on the machine’s lampboard.  This letter was recorded by a clerk for later transmission as part of an entire encoded message—a long series of letters and spaces.  Interestingly, the letter used as input was never the letter that would appear in the lampboard, which led to one of many ways to eliminate some of the multitude of letter possibilities and help crack Enigma’s code.

History of the Artifact
Polish cryptologists had worked to figure out the basics of Enigma code-breaking before WWII.  As the outbreak of war seemed imminent, the Poles passed along their data on the system to France and Great Britain.  At Bletchley Park, British mathematicians worked to create a primitive computer to look for weaknesses in the German code. 
A young man named Alan Turing designed a machine called a Bombe, judged by many to be the foundation of modern computing.  What might take a mathematician years to complete by hand, took the Bombe just 15 hours.  (Modern computers would be able to crack the code in several minutes).
Many of the weaknesses in the Enigma system came not from the apparatus itself, but from the people involved in using the code-generating machine.  Messages often began in predictable ways or contained weather reports that used similar words with regularity.  The fact that a letter entered in to the Enigma machine would never emerge from the maze of electrical contacts unchanged was also a valuable hint to cracking the code.
These clues, the cryptologists at Bletchley Park called them “cribs,” might change the possible outcomes of a scrambled message from billions to millions, allowing the Bombe to more quickly zero in on the correct solution.

Did you know?
By the end of the war, nearly every German Enigma message was being intercepted and decrypted within a day or two.  The impact of cracking Enigma is debated, but many believe that breaking the code advanced the end of World War II by years and saved countless lives.