Paper 2023/415

Maximally-Fluid MPC with Guaranteed Output Delivery

Giovanni Deligios, ETH Zurich
Aarushi Goel, NTT Research
Chen-Da Liu-Zhang, NTT Research

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 maximally-fluid MPC protocols that achieve security with {guaranteed output delivery}, 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. 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.

Note: The impossibility result in the previous version of our paper was incorrect. This is a revised version that does not include that result.

Available format(s)
Cryptographic protocols
Publication info
Fluid MPCinformation-theoretic
Contact author(s)
gdeligios @ ethz ch
aarushi goel @ ntt-research com
chendaliu @ gmail com
2023-06-10: revised
2023-03-22: received
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      author = {Giovanni Deligios and Aarushi Goel and Chen-Da Liu-Zhang},
      title = {Maximally-Fluid MPC with Guaranteed Output Delivery},
      howpublished = {Cryptology ePrint Archive, Paper 2023/415},
      year = {2023},
      note = {\url{}},
      url = {}
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