# Information Security and Cryptography Research Group

## Collusion-Free Multiparty Computation in the Mediated Model

### Joël Alwen, Jonathan Katz, Yehuda Lindell, Giuseppe Persiano, Abhi Shelat, and Ivan Visconti

Advances in Cryptology — CRYPTO 2009, Lecture Notes in Computer Science, Springer-Verlag, vol. 5677, pp. 524-540, Aug 2009.

Collusion-free protocols prevent subliminal communication (i.e., covert channels) between parties running the protocol. In the standard communication model, if one-way functions exist, then protocols satisfying any reasonable degree of privacy cannot be collusion-free. To circumvent this impossibility, Alwen, shelat and Visconti (CRYPTO 2008) 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 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., and resolve the main open questions in this area by showing a collusion-free protocol (in the mediated model) for computing any multi-party functionality.

## BibTeX Citation

@inproceedings{AKLPSV09,
author       = {Joël Alwen and Jonathan Katz and Yehuda Lindell and Giuseppe Persiano and Abhi Shelat and Ivan Visconti},
title        = {Collusion-Free Multiparty Computation in the Mediated Model},
editor       = {Shai Halevi},
booktitle    = {Advances in Cryptology --- CRYPTO 2009},
pages        = 524-540,
series       = {Lecture Notes in Computer Science},
volume       = 5677,
year         = 2009,
month        = 8,
publisher    = {Springer-Verlag},
}