The Security Requirement to Prevent Zero Dynamics Attacks and Perfectly Undetectable Cyber-Attacks in Cyber-Physical Systems

Abstract

The impacts of zero dynamics attacks and perfectly undetectable cyber-attacks cannot be observed in outputs of cyber-physical systems (CPS). Adversaries are capable of executing these cyber-attacks and leading the CPS to undesirable trajectories while remaining undetected. In this paper, we introduce and formally define the notion of security effort (SE) as a novel security metric for CPS that determines the minimum number of actuators and sensors that should be secured and kept attack free in order to prevent adversaries from executing zero dynamics attacks, covert attacks, and controllable attacks. Moreover, since zero dynamics attacks, covert attacks, and controllable attacks belong to weakly unobservable and controllable weakly unobservable subspaces of the CPS, conditions under which these subspaces become zero are obtained and investigated. An illustrative numerical simulation is provided to demonstrate the effectiveness of our proposed security measure.