Enigma

1
Enigma

• Meghan Emilio
• Faculty Sponsor Ralph Morelli
• (Computer Science)

2
Objective

• There are two main objectives of this project
• First, to create a working simulation of an
  Enigma machine that is as faithful as possible.
• Second, to create an analyzer which will break
  Enigma. That is, decrypt messages even if little
  or no information about the original settings is
  known.

3
What is Enigma?

• Electrical enciphering machine widely used by the
  German Military during WWII.
• Breaking Enigma a turning point of the war.
• Has three rotating rotors, a plugboard and a
  reflector.

4
Rotors and Plugboard

• The rotors rotate in the following sequence
• First rotor rotates each time a character is
  input.
• The second rotor rotates once each time the first
  rotor makes one full turn.
• The third rotor rotates once each time the second
  rotor has rotated completely.
• The plugboard provides a customizable swapping of
  pairs letters both before and after a character
  passed through the rotors.

5
Putting It All Together
Rotor I Swap
Plugboard Swap
Rotor II Swap
Rotor III Swap
Input
Output
Reflector Swap
6
Simulation

• Input English/Encrypted text and output Encrypted
  text/English
• Java Applet
• Faithful to rotor wirings and reflectors used
  during WWII

7
Analyzer

• Input encrypted text and output original English
  text
• No other input information is needed
• Assumes possession of an Enigma machine
• Assumes text was encrypted without a plug board
• Searches through possible decryptions using
  simulator and chooses the best one using Index of
  Coincidence (IC) as a scoring function

8
What is Index of Coincidence?

• Index of Coincidence (IC) is the probability that
  two randomly selected letters will be identical.
• IC is a statistical measure which distinguishes
  text encrypted polyalphabetically from text
  encrypted with a monoalphabetically.
• Every language has a calculated IC. For instance
  
• English 0.0667
• Random Text 0.0385

9
Why IC?

• Enigma encryptions are polyalphabetic
• This allows for a heuristic algorithm
• Instead of searching all possible decryptions,
  take the first one that comes close to 0.0667, as
  there should be only one.
• Effective on larger sample sizes (comparable to
  exhaustive search - see results)
• More efficient (relative to rotor setting - see
  results)

10
Problems with IC
11
Results
12
Conclusion

• A computer program was made that was able to
  break Enigma messages both efficiently and
  effectively.
• Modern day computers make it relatively easy to
  decrypt Enigma messages.
• Thus, Enigma is an inadequate form of encryption
  for the present day.