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 Rotor order  3x2x1 = 6 possible arrangements Swapping 6 letters  100,391,791,500 Approximately = 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. 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. Step 1:Step 2:

Ciphertext-Only Attack Step 1 Results

Ciphertext-Only Attack Step 1 Results Cont. # CharactersAvg. IOC Index out of 105, # CharactersSuccessful Decryptions

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.