The Enigma Machine

The Enigma machine was an electromechanical rotor machine that randomly replaced the letters of a message before sending it, ensuring that the message could only be read by its intended recipient.
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3 rotor Enigma machine. Click to enlarge.
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A Brief Overview of the Machine
Excerpt from Heroes of World War II: The Men Who Cracked Enigma
Excerpt from cryptanalyst Alan Turing's original notes, explaining the mechanical workings of the machine.
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The Impossible Code

The Germans learned from the Zimmermann Telegram and adopted the "unbreakable" Enigma machine in 1930 as the backbone for military and intelligence communications.

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1923 advertisement for a commercial Enigma, touting it as "unassailable." Click to enlarge

"Due to the special procedures performed by the Enigma machine, the solvability is so far removed from practical possibility that the cipher system ... must be regarded as virtually incapable of solution"
- German cryptographer


Click here or on the image to the right to learn how the Germans would code a message
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The machine's complexity created:
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Enigma Machine Simulator

How to use the simulator:

  1. Set the rotors to the desired setting (three random letters)
  2. Enter your message into the first textbox
  3. Click "Encipher" and your encoded message will appear in the box below

To decode a message, set the rotors to the same setting as they were when the message was originally enciphered. Click "Encipher" and your message will be decrypted back to the original message.

Rotor 3

Rotor 2

Rotor 1
Back: Breaking the Code

Thesis
Next: Polish Contributions

Glossary Page 1

Glossary Page 2

Ultra

"The secret British program to monitor and decipher Germany's Enigma signals"
- Sir Lawrence David Freedman, Professor of War Studies, King's College London


Enigma

“Three rotors, side by side, created an electrical maze. As they turned, they changed the maze - and thereby the encipherment. The result was a rather secure cipher”
- Dr. David Kahn, leading historian


Bletchley Park

“Bletchley Park was concentrated on deciphering, translating, evaluating and distributing the vast amount of information...transmitted by the Germans after they had been rendered 'secure' by encipherment on the famous Enigma machine”
- Ronald Lewin, British military historian


GCHQ

"After the war, it took over from the Government Code and Cipher School the function of receiving and decoding intercepted wireless traffic from listening stations scattered throughout the United Kingdom and from several dozen overseas"
- Lord Jonathan Sumption, British judge, author and medieval historian


Double Cross System

"For the duration of the war, brilliantly orchestrated false reports sent back to Germany by Masterman's tame agents would lead the German high command into one blunder after another at the most crucial junctures - ensuring the success of the Allied landing at Normandy, helping to turn the tide in the war against U-boats in the Atlantic, even tricking the Germans into firing most of their V-2 rockets short of central London"
- Stephen Budiansky, former national security correspondent, foreign editor, and deputy editor of U.S. News & World Report


Communications Intelligence (COMINT)

"COMINT is technical and intelligence information derived from foreign communications by other than the intended recipients"
- Department of Defense Directive, 2010


Signals Intelligence (SIGINT)

"Intelligence obtained through the interception of transmission signals"
- Merriam Webster Dictionary


Public Key Encryption


“A standard analogy for public-key cryptography is given as follows. Suppose that Bob has a wall safe with a secret combination lock known only to him and the safe is left open and made available to passers-by. Then anyone, including Alice, can put messages in the safe and lock it. However, only Bob can retrieve the message, since even Alice, who left a message in the box, has a way of retrieving the message.”
- Richard A. Mollin, author and professor