Overview of Opacity in Discrete Event Systems

In recent years, opacity has received increasing attention in terms of analyzing security and privacy problems. Opacity is a confidentiality property that characterizes a system's ability to hide its secret information from any external intruders. A systematic overview of opacity in the context of discrete event systems (DESs) was conducted; this paper firstly reviews the verification methods and computational complexity of the opacity in DESs using the formalisms of automata and Petri nets. When the system is verified to be non-opaque, the approaches that synthesize an opaque system are summarized. Finally, the future research directions and open problems of opacity in DES are also reviewed.