Co-Design of Watermarking and Robust Control for Security in Cyber-Physical Systems

TL;DR

This paper presents a unified framework for designing optimal watermarking signals and robust controllers in cyber-physical systems to enhance security against replay attacks while maintaining system performance.

Contribution

It introduces a joint design approach for watermarking and control that maximizes attack detection and minimizes performance loss, using convex optimization and LMI techniques.

Findings

Effective detection of replay attacks demonstrated on a three-tank system

Joint design improves security and robustness simultaneously

Method outperforms existing static control approaches

Abstract

This work discusses a novel framework for simultaneous synthesis of optimal watermarking signal and robust controllers in cyber-physical systems to minimize the loss in performance due to added watermarking signal and to maximize the detection rate of the attack. A general dynamic controller is designed to improve system performance with respect to the $\mathcal H_2$ norm, while a watermarking signal is added to improve security performance concerning the detection rate of replay attacks. The attack model considered in the paper is a replay attack, a natural attack mode when the dynamics of the system is unknown to the attacker. The paper first generalizes the existing result on the detection rate of $\chi^2$ detector from a static-LQR controller to a general dynamic controller. The design improvements on both robustness and security fronts are obtained by iteratively solving the convex subsets of the formulated non-convex problem in terms of the controller and watermarking signal. A semi-definite programming optimization is formulated using Linear Matrix Inequality (LMI) results to solve the larger system-level design optimization problem. We highlight the effectiveness of our method over a simplified three-tank chemical system.