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Secrecy and Security in Discrete-Event Systems

 The control theory of discrete-event systems (DESs) is a modeling framework for capturing the ordering of events or actions. Discrete-event systems modeling can be complementary to traditional continuous-time systems modeling or can be used alongside or in concert with continuous-time modeling in hybrid systems. Since decision-making is tantamount to prescribing which actions should or should not happen or which actions should happen before others, the body of work in DES theory is well-positioned to allow us to tackle security problems in cyber-physical systems. In this talk we present different approaches in DES control theory that address various problems in the security of systems and networks. In particular, we examine the notion of opacity, which is the property of ensuring that secret states or secret sequences of events are not discernible from non-secret states or events to a hostile agent. We also look at cases where systems are attacked by adversarial agents that manipulate sensor outputs (i.e., event occurrences generated by a plant) so that a supervisor (i.e., a DES controller) is fooled into thinking the system is in some state that it is not in. We discuss the challenges of modeling security and secrecy problems using discrete-event systems.