Stochastic Event-Triggered Feedback Physical Watermarks Against Replay Attacks

This paper considers the security of cyber-physical systems (CPSs) subject to replay attacks with measurements of the sensor transmitted to the remote estimator over a wireless communication network. We present a novel stochastic event-triggered feedback physical watermarking technique to effectively mitigate the impact of replay attacks, while simultaneously addressing the performance degradation caused by the inclusion of physical watermarks. This innovative approach dynamically adjusts the probability of adding physical watermarks based on the system's current operational state, striking a balance between optimal performance and effective countermeasures against replay attacks. And, as a result, the probability of adding physical watermarks increases when the system is subjected to malicious replay attacks. Furthermore, the performances of both the system and the detector are thoroughly characterized in two distinct scenarios: (i) the system operating under normal conditions, and (ii) the system being subjected to replay attacks. These scenarios allow for a comprehensive evaluation of the system's capabilities and the detector's efficacy in detecting and mitigating potential security threats. Finally, simulation examples are provided to corroborate and illustrate the theoretical results.