Combining Cryptography and Discrete-Event Systems to Study Sensor and Actuator Cyberattacks

We consider cyber-physical systems equipped with sensors and actuators controlled or monitored by software and communication capabilities. Such use of communication makes sensors and actuators possibly vulnerable to cyberattacks (more briefly: attacks). We consider two approaches to study sensor and actuator attacks. The cryptographic approach is to design each sensor and actuator to be invulnerable to attacks, regardless of the system in which it is deployed. The discrete-event system (DES)-based approach is to study the detection of sensor and actuator attacks by observing the behavior of the whole system, without adding any mechanism to sensors and actuators to make them invulnerable. In this paper, we introduce and compare the two approaches and suggest an efficient way to combine them. A concrete case study is presented.