A Polynomial Approach to Verifying the Existence of a Threatening Sensor Attacker

The development of cyber-physical systems (CPS) has brought much attention of researchers to cyber-attack and cyber-security. A sensor attacker targeting on a supervised discrete event system can modify a set of sensor readings and cause the closed-loop system to reach undesirable states. In this letter, we propose a new attack detection mechanism under which the supervisor only needs to keep track of the last observable event received. Given a plant and a supervisor enforcing a state specification, we define a sensor attacker threatening if it may cause the closed-loop system to enter a forbidden state. Our goal is to verify whether there exists such a threatening sensor attacker for a given controlled system. A new structure, called All Sensor Attack (ASA), is proposed to capture all possible sensor attacks launched by the attacker. Based on the ASA automaton, a necessary and sufficient condition for the existence of a stealthy threatening sensor attacker is presented. Finally, we show that the condition can be verified in polynomial time.