Opacity of Networked Supervisory Control Systems Over Insecure Communication Channels

In this article, we investigate security and privacy issues in networked supervisory control systems over multiple channel networks. We consider a networked discrete-event system controlled by a supervisor that receives information from sensors and sends control decisions to actuators via observation channels and control channels, respectively. The security problem is studied for the scenario where some of the communication channels are insecure in the sense there exists a passive intruder (eavesdropper) that can access the information-flow in those insecure communication channels. We adopt the concept of opacity, an information flow security property, to characterize the security status of the supervisory control system. Specifically, we assume that the system has a secret and the system is said to be opaque if the intruder can never determine the secret of the system unambiguously based on the information-flow in the insecure channels. We consider the notions of current-state opacity,
$K$
-step opacity, and infinite-step opacity in the networked control setting. New network observers are proposed to estimate the state of the system with two-side incomparable channel information. We show that the opacity verification problems for the networked setting can be effectively solved using the proposed network observers.