Anoop Sarkar SFU Computer Science

Zhelun Wu passes his MSc thesis exam

Zhelun Wu successfully defended his MSc thesis on July 20th 2016.

The title of the thesis: “Decipherment of Evasive or Encrypted Offensive Text”.

The abstract:

A very common computational task in monitoring online chat sessions is stopping users from sending malicious chat messages. Examples of malicious messages include age-inappropriate language, cyber-bullying, and sending out personal information. Rule based filtering systems are commonly used to deal with this problem, but not all of the malicious messages can be filtered out as people invent increasingly subtle ways to disguise their malicious messages to bypass such filtering systems. Machine learning classifiers can also be used to identify and filter malicious messages. However, such classifiers still rely on training data that becomes out of date and new forms of malicious text cannot be detected by the classifier. In this thesis, to solve this problem we model the messages corrupted by a malicious user to bypass a chat filter as a cipher text. We apply automatic decipherment techniques using Expectation-Maximization with Hidden Markov Models and a beam search algorithm in order to decrypt corrupted malicious text back into plain text which can be then filtered using rules or a classifier.

M.Sc. Examining Committee:

  • Dr. Anoop Sarkar, Senior Supervisor
  • Dr. Fred Popowich, Supervisor
  • Dr. David Alexander Campbell, External Examiner
  • Dr. Robert D. Cameron, Chair

More information on the Student theses page