The Enigma Encryption System

1
The Enigma Encryption System

• Andrew Regan
• CSC 290

2
Key Components for Encryption/Decryption

• Plugboard

• 3 Rotating Removable Rotors

• Reflector

3
Sample Encryption/Decryption
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Enigma
5
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

6
Ciphertext-Only Attack

• Developed by James Gillogly.

Step 1
Step 2

• 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.

• 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.

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Ciphertext-Only Attack Step 1 Results
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Ciphertext-Only Attack Step 1 Results Cont.
Characters Avg. IOC Index out of 105,456
50 19405.025
100 10059.05
150 2878.45
200 453.725
250 91.75
300 10.6
350 1.15
400 .2
450 .05
500 0
Characters Successful Decryptions
50 0.0
100 0.0
150 .1
200 .3
250 .475
300 .675
350 .875
400 .925
450 .975
500 1
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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.