A Self-Triggered Control Watermarking Scheme for Detecting Replay Attacks
B.G. Wolleswinkel (TU Delft - Team Riccardo Ferrari)
Riccardo M.G. Ferrari (TU Delft - Team Riccardo Ferrari)
M. Mazo (TU Delft - Team Manuel Mazo Jr)
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Abstract
We propose a novel watermarking scheme by modifying a self-triggered control (STC) policy, aimed at detecting replay attacks for linear time-invariant (LTI) systems. We show that by employing non-deterministic early triggering of the STC mechanism, replay attacks can be detected by a modified χ2 detector which takes into account the aperiodic nature of the inter-sample times. Specifically, we consider the case where a periodic reference signal is tracked, which makes these systems vulnerable to replay attacks. The proposed approach is modular and can be retrofitted to legacy systems. An approach for designing an online optimal early triggering mechanism is provided. This is validated through an illustrative numerical example in which we compare our method to scenarios employing both additive and multiplicative watermarking.