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Theory Seminar - Carsten Baum: Insured MPC: Efficient Secure Computation with Financial Penalties

Info about event

Time

Monday 1 April 2019,  at 15:00 - 16:00

Location

Nygaard-395 (5335-395), Åbogade 34, 8200 Aarhus N

About the speaker: Carsten Baum is a Postdoctoral Researcher at Bar Ilan University, Israel, under the supervision of Yehuda Lindell. Before joining Bar Ilan, he was a graduate student at the Computer Science Department of Aarhus University under the supervision of Ivan Damgård and Jesper Buus Nielsen (2013-2016).  Title: Insured MPC: Efficient Secure Computation with Financial Penalties

Title: Insured MPC: Efficient Secure Computation with Financial Penalties

Abstract: Fairness in Secure Multiparty Computation (MPC) is known to be impossible to achieve in the presence of a dishonest majority. Previous works have proposed combining MPC protocols with Cryptocurrencies in order to financially punish aborting adversaries, providing an incentive for parties to honestly follow the protocol. This approach also yields privacy-preserving Smart Contracts, where private inputs can be processed with MPC in order to determine the distribution of funds given to the contract. Unfortunately, the focus of existing work is on proving that this approach is possible and they present monolithic and mostly inefficient constructions. In this work, we put forth the first modular construction of ``Insured MPC'', where either the output of the private computation (which describes how to distribute funds) is fairly delivered or a proof that a set of parties has misbehaved is produced, allowing for financial punishments. Moreover, both the output and the proof of cheating are publicly verifiable, allowing third parties to independently validate an execution.

We present a highly efficient compiler that uses any MPC protocol  with certain properties together with a standard (non-private) Smart Contract and a publicly verifiable homomorphic commitment scheme to implement Insured MPC. As an intermediate step, we propose the first construction of a publicly verifiable homomorphic commitment scheme achieving composability guarantees and concrete efficiency. Our results are proven in the Global Universal Composability framework using a Global Random Oracle as the setup assumption. From a theoretical perspective, our general results provide the first characterization of sufficient properties that MPC protocols must achieve in order to be efficiently combined with Cryptocurrencies, as well as insights into publicly verifiable protocols. On the other hand, our constructions have highly efficient concrete instantiations, allowing for fast implementations.