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The exchange of sensitive information in many systems over a network can be manipulated by unauthorized access. Opacity is a property to investigate security and privacy problems in such systems. Opacity characterizes whether a secret information of a system can be inferred by an unauthorized user. One approach to verify security and privacy properties using opacity problem is to model the system that may leak confidential information as a discrete event system. We describe and analyze the complexity of opacity in systems that are modeled as a discrete event system with partial observation mapping. We define three types of opacity: strong opacity, weak opacity, and no opacity. Strong Opacity describes the inability for the system s observer to know what happened in a system. On the other hand, No-opacity refers to the condition where there is no ambiguity in the system behavior.

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Majed Ben-Kalefa received the Ph.D. degree in electrical engineering systems from Wayne State University, Detroit, in December, 2013. His research interests discrete event systems, and Model-Based Testing of Distributed Discrete Event Systems. He is currently on the Fuel Cell Research staff at Ford Company.

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