Sensor and Actuator Attacks of Cyber-Physical Systems: A Study Based on Supervisory Control of Discrete Event Systems

Cyber-physical systems (CPS) consist of physical processes that are controlled or monitored by software and communication capabilities. Sensors and actuators are elements of CPS that can be vulnerable to attacks. Sensor attacks typically consist in corrupting or hiding information received from sensors, or creating nonexisting information. Actuator attacks typically consist in intercepting and modifying orders sent to actuators. Attacks may lead to serious situations that we will call failures. We adopt a discrete event system (DES) approach, where information received from sensors and actions realized by actuators are represented as discrete events. We first develop a model of the attacked system using supervisory control of DES. Then, we study the defense viewpoint, where we develop methods to detect attacks and avoid failures, and determine conditions of attack detectability and failure avoidability. Then, we study the attacker’s viewpoint, where we develop a strategy based on supervisory control of DES to make the attacker undetectable.