Security and Fault Tolerance of Cyber-Physical Systems

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Critical infrastructures such as power grids, water supply systems, and traffic networks involve networked control systems with distributed sensors and actuators. We refer to them as cyber-physical systems. One key requirement for such systems is security from malicious attacks, often in the form of cyber-attacks aimed at compromising supervisory control and data acquisition (SCADA) systems. The second key requirement is fault tolerance: the ability of the control system to continue functioning despite component failures. Component failures can occur as a consequence of malicious actions by an attacker, but can also occur as a result of hardware breakdown or unforeseen operating conditions.***Most approaches to combat cyber-attacks focus on prevention through firewalls. With the advent of smart sensors and stealth technologies, preventing access and detecting intrusion are becoming increasingly difficult. There is an urgent need to develop counter-measures that can combat malicious intruders after intrusion has occurred. Traditional approaches to fault-tolerant control design are also inadequate as they often rely on first carrying out accurate fault diagnosis, followed by control reconfiguration. The system may be damaged or irrecoverable while waiting for diagnostic information. ***Our proposed research aims to improve the security and fault-tolerance of control systems central to cyber-physical systems. The two main objectives of our proposed research program are: (1) to develop novel methodology to detect malicious intruders and prevent them from inflicting damage to the control system; and (2) to maintain functionality and safe operation of control systems when components fail. ***The first objective focuses on security at the system level, typically involving SCADA systems describable using discrete event system models. Our methodology will make use of the theory of supervisory control and diagnosis for discrete event systems to perform intrusion detection and to counteract malicious behaviour. The novelty in our formulation is our focus on the control aspects after an intrusion has occurred, on how the feedback loop induces interactions between the actions of the attacker and defender.***The second objective focuses on resilience of the control system at the physical level when actuators and/or sensors fail. The novelty of our approach is that we focus on decentralized fault-tolerant control design which does not depend on accurate diagnostic knowledge. We propose to study fault-tolerant control as an integrated problem of distributed diagnosis and control reconfiguration, exploiting redundancies through coupling, and investigate network effects such as cascading failures. ***Protecting cyber-physical systems is of great national interest. Our proposed research can provide significant improvements on the security and resilience of cyber-physical systems.