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Sequential Probabilisitic Process Calculus and Simulation-Based Security

Anupam Datta, Ralf Küsters, John C. Mitchell, and Ajith Ramanathan

Several compositional forms of simulation-based security have been proposed in the literature, including universal composability, black-box simulatability, and variants thereof. These relations between protocols and ideal functionalities are similar enough that they can be ordered from strongest to weakest according to the logical form of their definitions. However, determining whether two relations are in fact identical depends on some subtle features that have not been brought out in previous studies. We identify the position of a ``master process'' in the distributed system, and some issues involving computational complexity and message forwarding, as two main factors. Using these distinctions, we prove necessary and sufficient conditions under which all notions are equivalent.