Comprehensively enhancing the security of control with combined homomorphic encryption

Homomorphic encryption is an effective way to address the privacy and security issues of Networked Control Systems (NCSs). Since the control function needs to be redesigned according to the homomorphism to complete encrypted computing, the practical implementation of a perfectly secure and highly efficient NCS is challenging. Previously proposed NCSs based on homomorphic encryption are still subject to the risk of eavesdropping attacks. In this paper, a combined homomorphic encryption scheme is designed to build a secure environment for NCSs. This scheme comprehensively enhances the security of NCSs by eliminating potential security hazards. The risk of eavesdropping attacks on information in the controller and communication channel is avoided. More specifically, the entire control scheme is encrypted and privacy computing within the controller is performed on this basis. Data protection is provided for all transmission channels, including the transmission of the intermediate result and controller state. In particular, the computational efficiency of the encrypted control system is fast and feasible for real-time control. The performance and stability of the closed-loop system are maintained.