Computers You Should Know

The Enigma Machine

Enigma machine in use, 1943

No other computer has the cloak of intrigue and the dagger of war surrounding it quite like the Enigma machine.

There were actually a whole family of Enigma coding-decoding machines produced. It was originally developed at the end of WWI and variants were used by a whole host of countries and businesses. However, it’s the Nazi use of the Enigma during WWII that has held the world in clouded wonder.

The Enigma is an electro-mechanical rotor machine that, with a set of daily settings and codebooks, allowed the user to encode a message. The settings included a wheel order, initial position of the rotors, a ring setting (sets the position of the alphabet ring with respect to the rotor), and keyboard plug settings. The same settings and codebooks were used on the other end to decode the message.

Procedures varied, even within the German military, but the machines were essentially the same. A set of rotors would turn as each key is pressed. When the key was pressed, the rotor would connect an electrical path that would encode the entered letter. The rotor would then turn again for the next input. For example, the “A” key is pressed once and it may be transmitted as “G” then the pressed again and transmitted as “C” due to the changes in one or more rotors. A graphic demonstrating this is here.

This system, along with the procedures put in place to operate it, was considered unbreakable by the Germans. However, even before WWII started it had been broken. The Polish Cipher Bureau cracked the code and, 5 weeks before WWII started, gave what they had learned to the English and French. As part of Operation Ultra, Allied codebreakers were able to read a great deal of the Nazi’s private mail. The capture of an Enigma machine on U-505, along with undestroyed codebooks, really put a dent in Hitler’s ability to send private love letters to Goebels and Braun.

[Image Credit: Bundesarchiv, Bild 183-2007-0705-502 / CC-BY-SA]

  • There's a very nice Enigma emulator for OS X here:

    Minutes of entertainment, until one realizes that it's pretty silly as a solo exercise.

    • The Professor

      Nonsense. I leave my self cryptic notes all of the time.

      • Same here, but I prefer to rely on the fact that my handwriting really is unbreakable.

        • The Professor

          Mine's fairly difficult to decode, but I had a graduate student once that was able to decipher it. I couldn't have that, so I started spilling various liquids randomly on my desk, mostly coffee and ginger ale, and that put a stop to it.

      • P161911

        Apparently you aren't the only one:

      • Alff

        Don't be so modest. You frequently send them to us.

      • pj134

        Dammit, you're good.

        Is the hyphen supposed to be after my or after self?

        The sentence is wholly unintelligible!

        • The Professor

          Ah, that was mainly from using the crappy, cheap keyboard that came with my new machine.

          • pj134

            Oh…. So it wasn't a master encryption?

  • Number_Six

    "My god, they've rearranged the keys! Has the Hun no scruples?!"

    • Even worse, some of the decrypted messages aren't in English! The scoundrels!

    • TurboBrick

      Just wait 'til you see a French AZERTY keyboard.

  • tonyola

    The one code that was never broken during WWII was the code talkers language based on the Navajo Indian language. It was used in the Pacific theater and the Japanese never figured it out, even when they tortured a captured Navajo who was not personally familiar with the code. Since it was strictly a spoken code and no machines were used, information could be passed along much faster than machine-based encryptions. The code was so effective that it was kept secret until 1968.

  • MrHowser

    So how did the Allies not tip their hand? I mean, if you're the Third Reich, and you're encoding lots of messages with this, and then all the plans based on those messages are foiled, wouldn't you think something was compromised?

    • The Professor

      Not with Herr Hitler in charge, if you wanted to keep your job. And head.

    • The key is the combination of "lots of messages" and "all the plans." Even with Enigma cracked, the Allies couldn't intercept everything, nor were the resources available to decrypt all of what was intercepted (at least not in a timely manner). Remember, by today's standards there was no real automation to all this, just a handful of hard-working people and a few machines. Worse, even when the info was in hand in time to do something with it, it still wouldn't have been possible to disrupt every known plan.

      The result, at least from the point of view of someone who "knew" Enigma couldn't be broken, was probably to conclude that the Allies had a reasonably effective conventional observation and espionage network and occasionally got a few lucky breaks. That's just the nature of war anyway, so it wouldn't have seemed unduly suspicious.

    • mr. mzs zsm msz esq

      It was still hard. So for example you needed to wait to capture some messages where there was a mistake, like the beginning was encoded twice, like a weather report at the beginning of two messages. With that they could figure-out the settings used that month for the rotors and connections. There were also different settings for the different branches of the German military. So some picking and choosing had to be done to decide on what to concentrate on deciphering each month.

  • domino_vitali

    one of my favorite topics, and a great article. thanks!

    silly Germans, everyone knows the only truly unbreakable code is that created by the one-time pad.

  • The Professor

    Didn't the Germans come up with a 5 rotor version towards the end of the war?

  • acarr260

    An enigma machine recently sold at auction for just over $200k (USD).

  • sport_wagon