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We present a model and protocol for anonymous credentials. Rather than using deterrents to ensure non-transferability, our model uses secure hardware with biometric authentication capabilities.Using the model combining biometric authentication with anonymous credentials in the wallet-with-observer architecture proposed by Bleumer [4], we formalize the requirements of an anonymous credential protocol. In doing so, we define what it means for a protocol to be strongly subliminalfree, and show that any protocol meeting this new definition can be used in a non-transferable anonymous credential system. Our new definition improves upon subliminal-freeness as used by Burmester et al [10], in that we restrict information flow among parties even when one party detects that others in the protocol are dishonest.We describe a new protocol which is strongly subliminalfree. We then extend this basic model in a modular way to include the additional feature that the issuing authority may revoke credentials via a single (broadcast) message. Finally, we present a second protocol in the extended model.

The article introduces a new formal system, the calculus of cooperation, for reasoning about coalitions of players in a certain class of games. The calculus is an extension of the propositional intuitionistic logic that adds a coalition parameter to intuitionistic implication. The system is shown to be sound and complete with respect to a game semantics.One intended application of the calculus of cooperation is the verification of privacy properties in multiparty computation protocols. The article argues that such properties can be established by providing a set of strategies for a non-zero-sum, perfect information game based on the protocol. It concludes with several examples of such verifications formalized in the calculus of cooperation. ACM Reference Format:Miner More, S. and Naumov, P. 2012. Calculus of cooperation and game-based reasoning about protocol privacy. ACM Trans. Comput.

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