[Resource Topic] 2023/1187: Broadcast-Optimal Two Round MPC with Asynchronous Peer-to-Peer Channels

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Title:
Broadcast-Optimal Two Round MPC with Asynchronous Peer-to-Peer Channels

Authors: Ivan Damgård, Divya Ravi, Luisa Siniscalchi, Sophia Yakoubov

Abstract:

In this paper we continue the study of two-round broadcast-optimal MPC, where broadcast is used in one of the two rounds, but not in both. We consider the realistic scenario where the round that does not use broadcast is asynchronous. Since a first asynchronous round (even when followed by a round of broadcast) does not admit any secure computation, we introduce a new notion of asynchrony which we call (t_d, t_m)-asynchrony. In this new notion of asynchrony, an adversary can delay or drop up to t_d of a given party’s incoming messages; we refer to t_d as the deafness threshold. Similarly, the adversary can delay or drop up to t_m of a given party’s outgoing messages; we refer to t_m as the muteness threshold.

We determine which notions of secure two-round computation are achievable when the first round is (t_d, t_m)-asynchronous, and the second round is over broadcast. Similarly, we determine which notions of secure two-round computation are achievable when the first round is over broadcast, and the second round is (fully) asynchronous. We consider the cases where a PKI is available, when only a CRS is available but private communication in the first round is possible, and the case when only a CRS is available and no private communication is possible before the parties have had a chance to exchange public keys.

ePrint: https://eprint.iacr.org/2023/1187

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