Perfect Stealthy Attacks in Cyber-physical Systems

Security of Cyber-Physical Systems (CPS) against cyber attacks is one of the most critical issues that should be investigated. In this paper, we deal with the vulnerabilities due to novel integrity cyber attacks named perfect stealthy attacks and the countermeasure against them in CPS which are modeled as a stochastic Linear Time-Invariant (LTI) system equipped with a Kalman filter, an LQG controller, and a χ2 failure detector. The attacks are designed by a sophisticated attacker so that the measurement residual of the compromised system coincides with the healthy one, and can ruin the system definitely. First, from an attacker's standpoint, we show an existence condition and a design procedure of the attacks using invariant subspace property. Then, on the other hand from a system supervisor's standpoint, the countermeasure against the malicious attacks using an aperiodic transmission scheme based on the Nash bargaining game is discussed. Finally, the dangerousness of the attacks and the effectiveness of the proposed detection method are verified through numerical simulations.