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The Enigma Encryption System. Andrew Regan CSC 290. Key Components for Encryption/Decryption. Plugboard. 3 Rotating Removable Rotors. Reflector. Sample Encryption/Decryption. Enigma. Enigma Properties. 3 rotors  26x26x26 = 17,576 initial settings

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The enigma encryption system

The Enigma Encryption System

Andrew Regan

CSC 290


Key components for encryption decryption
Key Components for Encryption/Decryption

  • Plugboard

  • 3 Rotating Removable Rotors

  • Reflector




Enigma properties
Enigma Properties

  • 3 rotors  26x26x26 = 17,576 initial settings

  • Rotor order  3x2x1 = 6 possible arrangements

  • Swapping 6 letters  100,391,791,500

  • Approximately 1016 = 10,000,000,000,000,000 keys

  • Later versions of the Enigma had even more keys.

    • Swapped more than 6 letters

    • Selected 3 rotors from set of 5


Ciphertext only attack

Developed by James Gillogly.

Find initial rotor setting and rotor order.

Uses Index of Coincidence.

Iterate through all possible initial rotor settings and rotor orders with no plugboard.

Largest IOC is the most likely rotor arrangement.

Ciphertext-Only Attack

Step 1:

Step 2:

  • Uses rotor settings from step 1.

  • Finds one new plugboard setting for each iteration.

  • Decrypt the text with every possible character pair.

    • 25x26 = 650 pairs.

  • Trigram analysis on the 650 decrypted texts. Add the setting to the plugboard with the best decrypted text.




Current trigram results
Current Trigram Results

  • Attempted analyzing text based on most probable trigrams in English plaintext.

    • +1 for “good” trigram, -1 for “bad.”

    • Highest score wins.

    • To many swaps initially to be accurate.

  • Currently working on developing trigram statistics for partially decrypted Enigma texts to use in the initial rounds of finding the plugboard settings.


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