An Expert System for Solving Simple Cryptograms Carolyn Rucci Dr. Ralph Morelli 1 year project.

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Presentation transcript:

An Expert System for Solving Simple Cryptograms Carolyn Rucci Dr. Ralph Morelli 1 year project

Overview Goal Background information What is an Expert System My Expert System - CipherExpert How does CipherExpert Work? Extensibility Results from testing Caesar Cipher

What? How? Goal Cryptanalysis techniques

Background Information dqdobvlv dqg ghflskhuph qw ri hqfubswhg phvvdjhv Cryptography Cryptanalysis Analysis and decipherm ent of encrypted messages

What is an Expert System? Reasons! CipherExpert

Hcrypto Analyzer classes (Java) Jess Expert System Main Java Class Hcrypto Decryption Classes (Java) Computer Science department libraries Prototype that uses a limited set of historical ciphers: Transposition, Caesar, Affine, Vigenere and Playfair Cipher Expert

How Does the Expert System Work? Distribution of Letter Frequencies Index of Coincidence

Easily Extensible Ciphers Substitution Simple- CaesarAffine Poly- PlayfairVigenere Transposition Rail FenceNew Cipher Add new classifications to family tree New rules New Cipher New Rules

Testing Tested CipherExpert 36 times, using 3 texts of varying length Determined CipherDecrypted Text Short Text (36 chars ) 10 / 12 Medium Text (500 chars) 11 / 1210 / 12 Long Text (1500 chars) 12 / 12 Overall 33 / 3632 / 36

Caesar Cipher abcdefghijklmnopqrstuvwxyz Ocdn dn v ozno oj nzz da ncjmo hznnvbzn rjmf. This is a test to see if short messages work. vwxyzabcdefghijklmnopqrstu Key = shift by 5 decipher

Advantages of an Expert System 1. More Efficient and accurate than other methods  Do not have to try all ciphers to find a decryption  No false positive decryptions 2. Analysis based on the frequencies of letters in the message  Distribution of letter frequencies  Index of coincidence

Java Main Class IndexOfCoincidence IOC(String) getIOC() : double Cipher Cipher(String) getShift() : int setCipher(String) getCipher() : String wkdwlvkr zlizrunv Text file Originally “unknown” IndexOfCoincidence IOC(String) getIOC() : double Cipher Cipher(String) getShift(): int setCipher(String) getCipher() : String Rete Java Main Class

Jess: Getting Started Search depth - 1 parent - no-parent ic - call getIOC() on object shift - call getShift() on object type - unknown last-move - no-move Create a template for initial position Fetch IndexOf Coincidence Object from rete

Jess: Example of Move to Substitution Rule Test shift <> 0 Search depth - 1 parent - no-parent ic shift - 4 type - unknown last-move - no-move Current_node true Matches node Creates new node Search depth - 2 parent - current_node ic shift - 4 type - unknown last-move - Substitution New_node

Jess: The Jess Path After each new node is created: 1) If type = knownRecognize cipher Return “last-move” of current node to Java 2) Else type unknownFurther solution Attempt to match another node