Geometrical Characterization of Sensor Placement for Cone-Invariant and Multi-Agent Systems against Undetectable Zero-Dynamics Attacks

TL;DR

This paper provides a geometric framework for sensor placement in cone-invariant and multi-agent systems to detect and defend against undetectable zero-dynamics attacks, enhancing cyber-physical security.

Contribution

It introduces a novel geometric characterization of zero-dynamics attacks and proposes a sensor placement strategy to detect such attacks efficiently.

Findings

Characterization of zero-dynamics attacks on cone-invariant systems.

Development of a sensor placement method for attack detection.

Identification of vulnerable actuator locations and sensor placement unions.

Abstract

Undetectable attacks are an important class of malicious attacks threatening the security of cyber-physical systems, which can modify a system's state but leave the system output measurements unaffected, and hence cannot be detected from the output. This paper studies undetectable attacks on cone-invariant systems and multi-agent systems. We first provide a general characterization of zero-dynamics attacks, which characterizes fully undetectable attacks targeting the non-minimum phase zeros of a system. This geometrical characterization makes it possible to develop a defense strategy seeking to place a minimal number of sensors to detect and counter the zero-dynamics attacks on the system's actuators. The detect and defense scheme amounts to computing a set containing potentially vulnerable actuator locations and nodes, and a defense union for feasible placement of sensors based on the geometrical properties of the cones under consideration.