Information Flow for Security in Control Systems

TL;DR

This paper develops an information flow analysis framework using KL divergence to evaluate and enhance the security and resilience of control systems against adversarial attacks in cyber physical systems.

Contribution

It extends information flow analysis methods from software security to control system security, introducing KL divergence as a causal measure of information flow.

Findings

KL divergence effectively quantifies adversarial influence on sensor outputs.

The framework relates information flow to attack detectability and stealthiness.

Active detection strategies can manipulate system inputs to reveal malicious behavior.

Abstract

This paper considers the development of information flow analyses to support resilient design and active detection of adversaries in cyber physical systems (CPS). The area of CPS security, though well studied, suffers from fragmentation. In this paper, we consider control systems as an abstraction of CPS. Here, we extend the notion of information flow analysis, a well established set of methods developed in software security, to obtain a unified framework that captures and extends system theoretic results in control system security. In particular, we propose the Kullback Liebler (KL) divergence as a causal measure of information flow, which quantifies the effect of adversarial inputs on sensor outputs. We show that the proposed measure characterizes the resilience of control systems to specific attack strategies by relating the KL divergence to optimal detection techniques. We then relate information flows to stealthy attack scenarios where an adversary can bypass detection. Finally, this article examines active detection mechanisms where a defender intelligently manipulates control inputs or the system itself in order to elicit information flows from an attacker's malicious behavior. In all previous cases, we demonstrate an ability to investigate and extend existing results by utilizing the proposed information flow analyses.