Distributing Keys and Random Secrets with Constant Complexity

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Abstract

In the Distributed Secret Sharing Generation (DSG) problem n parties wish to obliviously sample a secret-sharing of a random value s taken from some finite field, without letting any of the parties learn s. Distributed Key Generation (DKG) is a closely related variant of the problem in which, in addition to their private shares, the parties also generate a public “commitment” gs to the secret. Both DSG and DKG are central primitives in the domain of secure multiparty computation and threshold cryptography. In this paper, we study the communication complexity of DSG and DKG. Motivated by large-scale cryptocurrency and blockchain applications, we ask whether it is possible to obtain protocols in which the communication per party is a constant that does not grow with the number of parties. We answer this question to the affirmative in a model where broadcast communication is implemented via a public bulletin board (e.g., a ledger). Specifically, we present a constant-round DSG/DKG protocol in which the number of bits that each party sends/receives from the public bulletin board is a constant that depends only on the security parameter and the field size but does not grow with the number of parties n. In contrast, in all existing solutions at least some of the parties send Ω(n) bits. Our protocol works in the near-threshold setting. Given arbitrary privacy/correctness parameters 0<τpc<1, the protocol tolerates up to τpn actively corrupted parties and delivers shares of a random secret according to some τpn-private τcn-correct secret sharing scheme, such that the adversary cannot bias the secret or learn anything about it. The protocol is based on non-interactive zero-knowledge proofs, non-interactive commitments and a novel secret-sharing scheme with special robustness properties that is based on Low-Density Parity-Check codes. As a secondary contribution, we extend the formal MPC-based treatment of DKG/DSG, and study new aspects of Affine Secret Sharing Schemes.

Original languageEnglish
Title of host publicationTheory of Cryptography - 22nd International Conference, TCC 2024, Proceedings
EditorsElette Boyle, Mohammad Mahmoody
PublisherSpringer Science and Business Media Deutschland GmbH
Pages485-516
Number of pages32
ISBN (Print)9783031780226
DOIs
StatePublished - 2025
Event22nd Theory of Cryptography Conference, TCC 2024 - Milan, Italy
Duration: 2 Dec 20246 Dec 2024

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume15367 LNCS

Conference

Conference22nd Theory of Cryptography Conference, TCC 2024
Country/TerritoryItaly
CityMilan
Period2/12/246/12/24

Keywords

  • Distributed Key Generation
  • Secret Sharing
  • Secure Computation

All Science Journal Classification (ASJC) codes

  • Theoretical Computer Science
  • General Computer Science

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