Risk-Based Scheduling of Security Tasks in Industrial Control Systems With Consideration of Safety

Industrial control systems (ICSs) in networked environments face severe cyber-security risks and challenges. A timely response to cyber-attacks is of paramount importance for mitigating risks. However, the security policy developed for an ICS may be conflicting with the ICS's safety policy, on which much attention has been paid for a long time in industrial control. An inappropriate enforcement of the security policy may deteriorate the ICS performance or even result in severe unexpected consequences. To tackle this problem, a risk-based security task scheduling approach is presented for ICSs with consideration of the safety policy. It ensures a timely response to cyber-attacks without compromising safety. More specifically, the approach reconciles security tasks and safety tasks according to a designed resolution policy, so as to acquire contradiction-free security and safety (S&S) tasks. Then, a real-time risk assessment method is developed to characterize the subtle change of the system risk with the implementation of the reconciled S&S tasks. After that, a task scheduling method is designed with the risk as the optimization objective, i.e., it searches the optimal task scheduling scheme by minimizing the risk posture. The resulting scheduling scheme ensures the smooth implementation of the S&S policy, which reflects the optimal recovery process against the risk. Finally, case studies on a hardware-in-the-loop testbed are conducted to demonstrate the effectiveness of the proposed approach.