International Association
for Cryptologic Research

Nicolas Alhaddad , Boston University

Mayank Varia , Boston University

Ziling Yang , University of Illinois Urbana-Champaign

DOI: 10.62056/a0qj5w7sf

URL: https://cic.iacr.org/p/1/4/3

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Asynchronous complete secret sharing (ACSS) is a foundational primitive in the design of distributed algorithms and cryptosystems that require confidentiality. ACSS permits a dealer to distribute a secret to a collection of N servers so that everyone holds shares of a polynomial containing the dealer's secret.

This work contributes a new ACSS protocol, called Haven++, that uses packing and batching to make asymptotic and concrete advances in the design and application of ACSS for large secrets. Haven++ allows the dealer to pack multiple secrets in a single sharing phase, and to reconstruct either one or all of them later. For even larger secrets, we contribute a batching technique to amortize the cost of proof generation and verification across multiple invocations of our protocol.

The result is an asymptotic improvement in the worst-case amortized communication and computation complexity, both for ACSS itself and for its application to asynchronous distributed key generation. Our ADKG based on Haven++ achieves, for the first time, an optimal worst case amortized communication complexity of κN without a trusted setup. To show the practicality of Haven++, we implement it and find that it outperforms the work of Yurek et al. (NDSS 2022) by more than an order of magnitude when there are malicious, faulty parties.