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Opacity Generalized to Transition Systems

Recently, opacity has proved to be a very promising technique for describing security properties. Much of the work has been couched in terms of Petri nets. Here, we extend the notion of opacity to the model of labelled transition systems and generalize opacity in order to be able to represent information flow security as well as protocol security. We give precise links between opacity and other information flow security definitions such as anonymity or non-interference and between opacity and formal methods applied to protocols in the case of a bounded number of sessions. We also detail a safe way to approximate initial opacity in the case of Petri nets that allows efficient checking of opacity. We illustrate this by two examples, one describing anonymity in a commercial context and the other modelling requirements upon a simple vote system.