Welcome to the resource topic for 2023/415
Title:
Maximally-Fluid MPC with Guaranteed Output Delivery
Authors: Giovanni Deligios, Aarushi Goel, Chen-Da Liu-Zhang
Abstract:To overcome the limitations of traditional secure multi-party computation (MPC) protocols that consider a static set of participants, in a recent work, Choudhuri et al. [CRYPTO 2021] introduced a new model called Fluid MPC, which supports {\em dynamic} participants. Protocols in this model allow parties to join and leave the computation as they wish. Unfortunately, known fluid MPC protocols (even with strong honest-majority), either only achieve security with abort, or require strong computational and trusted setup assumptions.
In this work, we also consider the “hardest” setting — called the maximally-fluid model — where each party can leave the computation after participating in a single round. We study the problem of designing information-theoretic maximally-fluid MPC protocols that achieve security with guaranteed output delivery (without relying on trusted setup), and obtain the following main results:
(1) We design a perfectly secure maximally-fluid MPC protocol, that achieves guaranteed output delivery against unbounded adversaries who are allowed to corrupt less than a third of the parties in every round/committee.
(2) We show that the corruption threshold in the above protocol is optimal. In particular, we prove that in fluid MPC, when the adversary can corrupt a third (or more) of the parties in any round, it is impossible to achieve information-theoretic security and guaranteed output delivery simultaneously — even assuming a common random string (CRS) setup.
Additionally, for the case where the adversary is allowed to corrupt up to half of the parties in each committee, we present a new computationally secure maximally-fluid MPC protocol with guaranteed output delivery. Unlike prior works that require correlated setup and NIZKs, our construction only uses a common random string setup and is based on linearly-homomorphic equivocal commitments.
ePrint: https://eprint.iacr.org/2023/415
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