A Superb Cryptanalytical Guide to the Enigma Cipher Machine

Over the years I’ve come across many articles explaining how the Enigma cipher machine works. All too often I would feel, as a cryptanalyst, that many of the articles glossed over important features or handled them poorly.

Well, if you’re looking for an in-depth explanation of the Enigma, complete with a lucid mechanical description and mathematical underpinnings you can really sink your teeth into (and understand!) look no further. Check out Erik Vestergaard’s superb explanation of the Enigma’s mechanical, operational, and mathematical aspects. A Danish high school mathematics teacher, Vestergaard took his class on a study tour to London in 2007, and one of their stops included Bletchley Park. This site is a wonderful compilation of their experience in Bletchley, complete with mouth-watering, clear descriptions of how the Enigma works and how it was broken. Here’s a list of topics covered:

1. Introduction
2. The situation before Enigma – history briefly
3. How Enigma works
   1. Ring settings
   2. The notch
   3. Rotor arrangements
   4. Rotor settings
   5. Double stepping
   6. Plugboard settings
   7. Reciprocal property
4. Marian Rejewski and the Poles
5. Double encryption
   1. Daily key from the Code Book
   2. Message key
6. The mathematics used by the Poles
7. An article from Mathematics Magazine
   1. Polish Mathematicians Finding Patterns in Enigma Messages (861 kB)
   2. The mathematics behind the solution of Enigma (a guiding document) (165 kB)
8. The Bletchley Park era
9. The decryption procedure at Bletchley Park
10. Cribs
11. The Turing bombe
12. Enigma and the Turing Bombe in Excel VBA
    1. Enigma simulator in Excel VBA (101 kB)
    2. Turing Bombe simulator in Excel VBA (210 kB)
13. Our visit at Bletchley Park
14. Interactive resources/simulators
15. Links
16. Online literature
17. Film
18. Literature

Doubtless, Erik has left his students with an indelible love for history and mathematics. Man, I wish I had a math teacher like this when I was in high school.

Enjoy!