Paper 2023/1793

Accountable Multi-Signatures with Constant Size Public Keys

Abstract

A multisignature scheme is used to aggregate signatures by multiple parties on a common message $m$ into a single short signature on $m$. Multisignatures are used widely in practice, most notably, in proof-of-stake consensus protocols. In existing multisignature schemes, the verifier needs the public keys of all the signers in order to verify a multisignature issued by some subset of signers. We construct new practical multisignature schemes with three properties: (i) the verifier only needs to store a constant size public key in order to verify a multisignature by an arbitrary subset of parties, (ii) signature size is constant beyond the description of the signing set, and (iii) signers generate their secret signing keys locally, that is, without a distributed key generation protocol. Existing schemes satisfy properties (ii) and (iii). The new capability is property (i) which dramatically reduces the verifier's memory requirements from linear in the number of signers to constant. We give two pairing-based constructions: one in the random oracle model and one in the plain model. We also show that by relaxing property (iii), that is, allowing for a simple distributed key generation protocol, we can further improve efficiency while continuing to satisfy properties (i) and (ii). We give a pairing-based scheme and a lattice-based scheme in this relaxed model. Our pairing based constructions are closely related to a multisignature scheme due to Boneh, Drijvers, and Neven (Asiacrypt 2018), but with several key differences.