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Enigma

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Has three rotating rotors, a plugboard and a reflector. Rotors and Plugboard ... The second rotor rotates once each time the first rotor makes one full turn. ... – PowerPoint PPT presentation

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Title: 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.
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