Dynamic Watermarking for General LTI Systems
For control system security, this work addresses a gap by enabling attack detection in general LTI systems, though the method is incremental as it builds on prior dynamic watermarking approaches.
This paper extends dynamic watermarking for attack detection to general MIMO LTI systems with partial state observations, providing asymptotic and statistical tests that detect sensor attacks more general than replay attacks. Simulations on autonomous vehicles demonstrate the approach can distinguish sensor attacks from wind disturbance.
Detecting attacks in control systems is an important aspect of designing secure and resilient control systems. Recently, a dynamic watermarking approach was proposed for detecting malicious sensor attacks for SISO LTI systems with partial state observations and MIMO LTI systems with a full rank input matrix and full state observations; however, these previous approaches cannot be applied to general LTI systems that are MIMO and have partial state observations. This paper designs a dynamic watermarking approach for detecting malicious sensor attacks for general LTI systems, and we provide a new set of asymptotic and statistical tests. We prove these tests can detect attacks that follow a specified attack model (more general than replay attacks), and we also show that these tests simplify to existing tests when the system is SISO or has full rank input matrix and full state observations. The benefit of our approach is demonstrated with a simulation analysis of detecting sensor attacks in autonomous vehicles. Our approach can distinguish between sensor attacks and wind disturbance (through an internal model principle framework), whereas improperly designed tests cannot distinguish between sensor attacks and wind disturbance.