the enigma encryption system andrew regan csc 290
Post on 21-Dec-2015
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The Enigma Encryption The Enigma Encryption SystemSystem
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 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 AttackDeveloped 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.
( 1)
( 1)
z
i ii a
f fIC
N N
• 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
0
20000
40000
60000
80000
100000
120000
50 100 150 200 250 300 350 400 450 500
Number of Characters
Index of IOC
t01t02t03t04t05t06t07t08t09t10t11t12t13t14t15t16t17t18t19t20t21t22t23t24t25t26t27t28t29t30t31t32t33t34t35t36t37t38t39t40
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
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.