Intrusion Detection in Controlled Discrete Event Systems

The constituent controllers in a supervisory control system may sometimes fail as a result of an intruder interfering with the feedback performance of the system. The intrusion may allow the system to execute traces that the supervisor wishes to prevent from occurring. We derive conditions under which a supervisor can detect the presence of an intruder in time to prevent the execution of an illegal trace. In situations where it is not possible to block all illegal strings, we use a language measure method to assess the damage caused by a particular set of controllers failing. We also use the language measure technique to determine the optimal behavior of the controlled system in the presence of an intrusion