Switching multiplicative watermark design against covert attacks

TL;DR

This paper introduces an optimal switching multiplicative watermark design for cyber-physical systems to improve attack detection, minimizing attacker impact through adaptive parameter optimization.

Contribution

It proposes a novel optimal design strategy for switching watermark filters based on output-to-output gain, enhancing attack detectability in CPS.

Findings

The algorithm provides optimal next-step parameters for watermark filters.

Simulation results show reduced attacker impact with the proposed method.

The approach allows for randomized watermark parameters to increase stealthiness.

Abstract

Active techniques have been introduced to give better detectability performance for cyber-attack diagnosis in cyber-physical systems (CPS). In this paper, switching multiplicative watermarking is considered, whereby we propose an optimal design strategy to define switching filter parameters. Optimality is evaluated exploiting the so-called output-to-output gain of the closed loop system, including some supposed attack dynamics. A worst-case scenario of a matched covert attack is assumed, presuming that an attacker with full knowledge of the closed-loop system injects a stealthy attack of bounded energy. Our algorithm, given watermark filter parameters at some time instant, provides optimal next-step parameters. Analysis of the algorithm is given, demonstrating its features, and demonstrating that through initialization of certain parameters outside of the algorithm, the parameters of the multiplicative watermarking can be randomized. Simulation shows how, by adopting our method for parameter design, the attacker's impact on performance diminishes.