Covert attack detection for cyber-physical systems using input-associated watermarking mechanism

In this paper, a novel covert attack detector is developed for cyber–physical systems by using input-associated watermarking mechanism. Covert attacks are very sophisticated and rely on perfect model knowledge, so that the generated attack signals have no response in the measurement output and thus evades the standard ${\chi }^2$ detector. A necessary and sufficient condition and a sufficient condition are respectively presented for the stealthiness and destructiveness of covert attacks for the purpose of revealing the features of covert attacks. Then, a novel input-associated watermarking mechanism is developed to assist ${\chi }^2$ detector to “expose” the attack behaviors in the detection process. Intensive analysis is subsequently implemented on the resultant attack detection rate under the proposed detection mechanism. It is worth emphasizing that the developed detection mechanism does not sacrifice the estimation performance under the attack-free situation. Furthermore, the designed proactive detection method is extended to the detection for the so-called zero dynamics attacks. Ultimately, a simulation example is utilized to illustrative the usefulness and effectiveness of the proposed input-associated watermarking mechanism.