Cyber-Physical Control With Delay-Induced Feedback Watermarking
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Solution Overview
Problem
Cyber-physical systems are vulnerable to replay attacks due to the incorporation of watermarking signals that degrade system performance, necessitating a method to enhance security without significant performance loss.
Innovation Solution
A time-delayed state-estimate watermarking scheme is employed, where past system states are randomly delayed and scaled to generate watermarking signals, ensuring they are within admissible input ranges to prevent system instability and facilitate fast attack detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If watermarking signals are incorporated into the control system to detect replay attacks, then security against replay attacks is improved, but system performance degrades due to the additional noise
Solution Approach 1:
The patent changes the fundamental parameter of the watermarking signal from additive noise to time-delayed feedback. By modifying the signal type and its temporal characteristics, the system achieves replay attack detection while minimizing performance degradation. The time-varying delay parameter allows the watermark to be adaptive rather than static noise.
Solution Approach 2:
The patent implements feedback by using past system outputs as the source of the watermarking signal. The watermark is generated from delayed feedback of the actual system behavior, creating a dynamic authentication mechanism that adapts to system changes while maintaining security. This feedback-based approach replaces static noise with adaptive signal generation.
2Measurement precision
If the watermarking signal intensity is increased to improve detection accuracy, then replay attack detection capability is improved, but system stability may be compromised
Solution Approach 1:
The patent applies dynamics by making the watermarking signal time-varying through random delay adjustments. The delay parameter changes over time according to a probability distribution, creating a dynamic watermark that adapts to system conditions. This dynamic approach allows the system to maintain detection accuracy while avoiding the stability issues associated with fixed-intensity watermarks.
Solution Approach 2:
The patent uses partial action by applying watermarking only to specific portions of the control signal through time-delayed feedback. Rather than continuously applying full-strength watermarking, the system uses probabilistic delay selection to apply watermarking selectively, achieving sufficient detection accuracy while minimizing impact on system stability.
Data Source
AI summary
A system and a method for secure control of a physical system are described. During operation, the system can obtain measurement of one or more sensors associated with the physical system. The system then estimates a state of the physical system based on the measurement of the sensors. Subsequently, the system generates a feedback control signal based on the estimated state and generates a watermarking signal based on a stored estimated state of the physical system at a previous time instant. The system then generates a watermarked control signal by combining the feedback control signal and the watermarking signal and applies the watermarked control signal to the physical system to regulate the state of the physical system, thereby facilitating secure control of the physical system.