Cyber-security enhancement of networked control systems using homomorphic encryption

This paper proposes a new concept of controller encryption for enhancement of the cyber-security of networked control systems and presents how to encrypt a linear controller using our modified homomorphic encryption schemes based on public-key RSA and ElGamal encryption systems. A remarkable advantage of the controller encryption is to be able to conceal several informations processed inside the controller device, such as controller parameters, references (recipes), measurements, control commands, and parameters of plant models in the internal model principal, maintaining an original function of the controller. Therefore, even if malicious users hacked the controller device by unauthorized accesses, it would take much time and cost to decipher and steal the control system's information. Finally, numerical examples confirm that only the scrambled parameters and signals can be seen in the controller device of the security-enhanced networked control system.