[Resource Topic] 2020/740: Always Have a Backup Plan: Fully Secure Synchronous MPC with Asynchronous Fallback

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Always Have a Backup Plan: Fully Secure Synchronous MPC with Asynchronous Fallback

Authors: Erica Blum, Chen-Da Liu-Zhang, Julian Loss


Protocols for secure Multi-Party Computation (MPC) can be classified according to the underlying communication model. Two prominent communication models considered in the literature are the synchronous and asynchronous models, which considerably differ in terms of the achievable security guarantees. Synchronous MPC protocols can achieve the optimal corruption threshold n/2 and allow every party to give input, but become completely insecure when synchrony assumptions are violated. On the other hand, asynchronous MPC protocols remain secure under arbitrary network conditions, but can tolerate only n/3 corruptions and parties with slow connections unavoidably cannot give input. A natural question is whether there exists a protocol for MPC that can tolerate up to t_s < n/2 corruptions under a synchronous network and t_a < n/3 corruptions even when the network is asynchronous. We answer this question by showing tight feasibility and impossibility results. More specifically, we show that such a protocol exists if and only if t_a + 2t_s < n and the number of inputs taken into account under an asynchronous network is at most n-t_s.

ePrint: https://eprint.iacr.org/2020/740

Talk: https://www.youtube.com/watch?v=01c3uQCBuNc

Slides: https://iacr.org/submit/files/slides/2020/crypto/crypto2020/222/slides.pdf

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