International Association for Cryptologic Research

International Association
for Cryptologic Research


Chopsticks: Fork-Free Two-Round Multi-Signatures from Non-Interactive Assumptions

Jiaxin Pan , NTNU
Benedikt Wagner , CISPA Helmholtz Center for Information Security and Saarland University
DOI: 10.1007/978-3-031-30589-4_21 (login may be required)
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Presentation: Slides
Conference: EUROCRYPT 2023
Abstract: Multi-signatures have been drawing lots of attention in recent years, due to their applications in cryptocurrencies. Most early constructions require three-round signing, and recent constructions have managed to reduce the round complexity to two. However, their security proofs are mostly based on non-standard, interactive assumptions (e.g. one-more assumptions) and come with a huge security loss, due to multiple uses of rewinding (aka the Forking Lemma). This renders the quantitative guarantees given by the security proof useless. In this work, we improve the state of the art by proposing two efficient two-round multi-signature schemes from the (standard, non-interactive) Decisional Diffie-Hellman (DDH) assumption. Both schemes are proven secure in the random oracle model without rewinding. We do not require any pairing either. Our first scheme supports key aggregation but has a security loss linear in the number of signing queries, and our second scheme is the {first} tightly secure construction. A key ingredient in our constructions is a new kind of homomorphic dual-mode commitment scheme for group elements, that allows to equivocate for messages of a certain structure. The definition and efficient construction of this commitment scheme is of independent interest. It is the first such commitment scheme for group elements from the plain DDH assumption without pairings.
  title={Chopsticks: Fork-Free Two-Round Multi-Signatures from Non-Interactive Assumptions},
  author={Jiaxin Pan and Benedikt Wagner},