Coding control signals and switching LQG controller for secure fault-tolerant control against stealthy false data injection

Security of Cyber-Physical Systems (CPS) against Cyber attacks has become an important challenging research field. False data injections on control and/or measurement signals of a Fault-Tolerant Control System (FTCS) can be treated as detectable virtual actuator or sensor faults. In this case, the FTCS can automatically accommodate false data injections by triggering the controller reconfiguration mechanism at detection time given by the mode-based Fault Detection and Isolation (FDI) algorithm. We show that an intelligent adversary can destabilize the non minimum phase plant of the FTCS by designing a false data injection attack on the control signal while remaining undetectable from any passive FDI algorithm. By using a confining coding method able to block the attack signal on a minimum number of encoded control signals, this paper proposes to transform stealthy false data injections into detectable attacks from an active FTCS based on a switching Linear Quadratic Gaussian (LQG) controller.