A Study Of Opacity In A Class Of Discrete Event Systems

With the rapid development and application of information technology, today’s society has been completely informationized. And in all aspects of people’s works or lives, every moment, information will be generated and disseminated quickly and widely. Thus information security has become an important issue of individual, institutions or countries.From the view of protecting considered objectives, information security is divided into security of the content or the dissemination mechanism of information. The object of this paper is information dissemination mechanism. From the perspective of event-driven, information dissemination mechanism can be abstract to discrete event systems and then to build graphical mathematical models using automata and Petri nets. Based on these models, analysis, control and optimization will be operated. Specific work in this paper has two parts, namely research of events opacity and state opacity, respectively.The first part of the paper studies event opacity. There are general phenomena in real lives or works that we need to protect an individual’s personal conducts, important business or strategic decision-making of one company or some other military disposition of countries not to be uncover by competitors or peripheral world. In this chapter, these private actors, as well as other important decisions and strategic, are abstracted into sets of occult events in discrete event systems which are modeled by finite state automata. Based on this, we propose the concept of event opacity. By taking into account the timeliness of private information, we accordingly propose k step event opacity. Verification algorithms are provided that are based on the operations on automata. Before operating, we need construct automata containing the features of conceal information. The main contribution of this chapter is that, in the framework of automata, propose two concepts of event opacity and k step opacity and the corresponding verification algorithms. Under the background that there already exists the concept of language opacity in the high level of language and state opacity in the level of constitution elements of automata, event opacity whose objective are also oneof the basic constitution elements of automata plays a important role from the completeness of notions.The second part of the study of this article is about verification algorithms of state opacity based on a special kind of Petri nets. In the existing state opacity verification algorithm in Petri net models, most works are about generic Petri nets and few researchers work on specific nets by using their unique characteristics to develop more efficient algorithms. In this paper, we consider one kind labeled Petri nets, whose unobservable sunset is acyclic. The special advantage of this net is that we can use basis markings and state equations based on basis markings to equivalent marking graph of this kind nets, just like the observers in the framework of automata. Comparing to existing checking algorithms, we do not need to enumerate all the possibilities, which is the greatest advantage of our approach.Totally say, our main contribution is to propose the concepts of event opacity and provide relevant verification algorithms in the models of automata and apply the technique of basis marking to design verification algorithms with high efficiency for one specific Petri nets.