Watermark Detection Method For Covert Replay Attack In Networked Control System

Network attack detection is a hot topic in the security research of networked control system(NCS).Research has found that replay attacks are concealed in stable NCS.At present,the watermark detection technology is often used to detect covert replay attacks.This technology identifies attack behaviors by adding a watermark signal to the optimal control quantity of the system.The watermark signal is usually an independent and identically distributed Gaussian noise sequence,which will cause a certain performance loss to the control system.This article mainly studies the detection of covert replay attacks,improves and extends the watermark detection technology to adapt it to more complex control environments.First,the concealment principle of the replay attack and the theoretical basis of the watermark detection technology is explained in detail,and the influence of the replay attack on the stability of the closed-loop system is analyzed.Secondly,aiming at the problem that the slow-process controlled object is "insensitive" to the high-frequency watermark,a smooth watermark detection technology is proposed.This technology uses sampling and interpolation algorithms to "smooth" the watermark signal to adapt it to the large inertia characteristic of the slow process.The simulation results show that this method performs well in slow processes,which can effectively improve the attack detection effect while reducing the additional performance loss of the system.Then,aiming at the problem of system performance degradation caused by the use of the watermark detection technology,a symmetric watermark encryption technology that uses watermark signal as a key to encrypt sensor data is designed.The symmetric encryption and decryption process will not cause additional performance loss to the system.The cracking method of the symmetric watermark encryption technology is given,and an asymmetric watermark encryption technology with higher security performance is proposed.Simulation results show that the symmetric watermark encryption technology can effectively detect covert replay attacks without affecting system performance;the asymmetric watermark encryption technology can effectively prevent malicious cracking while detecting replay attacks.Finally,a four-tank liquid level control system is used to simulate NCS,and physical experiments of replay attack detection are carried out.Experimental results show that the smooth watermark detection technology has a better performance than the traditional one on the large inertia four-tank plant;the watermark encryption technology can effectively detect covert replay attacks,and asymmetric encryption has higher security.The methods mentioned in this article are both feasible and practical.