Cryptology ePrint Archive: Report 2008/533

Collusion-Free Multiparty Computation in the Mediated Model

Jonathan Katz and Yehuda Lindell

Abstract: Collusion-free protocols prevent subliminal communication (i.e., covert channels) between parties running the protocol. In the standard communication model (and assuming the existence of one-way functions), protocols satisfying any reasonable degree of privacy cannot be collusion-free. To circumvent this impossibility result, Alwen et al. recently suggested the mediated model where all communication passes through a mediator; the goal is to design protocols where collusion-freeness is guaranteed as long as the mediator is honest, while standard security guarantees continue to hold if the mediator is dishonest. In this model, they gave constructions of collusion-free protocols for commitments and zero-knowledge proofs in the two-party setting.

We strengthen the definition of Alwen et al. in several ways, and resolve the key open questions in this area by showing a collusion-free protocol (in the mediated model) for computing any multi-party functionality.

Category / Keywords: cryptographic protocols / secure computation

Date: received 19 Dec 2008

Contact author: jkatz at cs umd edu

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Version: 20081219:223736 (All versions of this report)

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