Secret Protection in Discrete-Event Systems With Generalized Confidentiality Requirements

Abstract

In this article, we propose a general framework to design optimal secret protection policies in discrete-event systems. The system is modeled by an automaton in which several states are secret and assigned with different confidentiality requirement. Events in the system can be protected to verify the identity of the user, and a user who successfully executes/passes a protected event gains some authorization. Our purpose is to design an event-protecting policy such that any user, either legal or unauthorized, who visits a secret state must have an authorization that satisfies the requirement of confidentiality of the state. We consider the criteria of optimality on protecting policies as to protecting policies with a minimum degree of disturbance to legal users' normal operations. To this aim, we use Moore machines to model the dynamics of the clearance level of users when using the system. Then, we develop an auxiliary data structure called the generalized secret automaton, based on which we propose a method to design a protecting policy using the classical supervisory control theory. The minimally disruptive protecting policy is then represented by an automaton called the secret enforcer whose state size is polynomial both in the number of the plant states and the number of secret states in the plant.