Byzantine Fault-Tolerant Post-Quantum Distributed Quorum Signatures

Quentin Kniep; Jakub Sliwinski; Roger Wattenhofer

Byzantine Fault-Tolerant Post-Quantum Distributed Quorum Signatures

Distributed, Parallel, and Cluster Computing 2026-07-20 v1

Authors: Quentin Kniep , Jakub Sliwinski , Roger Wattenhofer

Abstract

Threshold, aggregate, and multi-signatures -- which we collectively call quorum signatures -- certify that a quorum of nodes endorsed a statement, with a certificate as small as a single signature. No constant-size post-quantum quorum signature is known: all candidates grow with the number of signers and are slow to aggregate, making quorum signatures the hardest obstacle to migrating byzantine fault-tolerant systems to post-quantum security. In this paper, we sidestep this open cryptographic problem by changing how the protocol communicates. We introduce a primitive we call Distributed Quorum Signature (DQS), built solely from ordinary digital signatures and a Bracha-style approval broadcast. DQS turns certificates from network messages into local events. Two event types divide the roles certificates play: weak certificates capture safety, strong certificates capture liveness. In DQS every message is constant size, fitting a single datagram regardless of the number of nodes. The total communication is quadratic, and no security assumptions change. In a large distributed system, the overhead of post-quantum DQS is competitive with the canonical pre-quantum BLS scheme.

Keywords

byzantine fault tolerance post-quantum cryptography quorum signatures distributed signatures broadcast protocol constant-size certificates

Cite

@article{arxiv.2607.17700,
  title  = {Byzantine Fault-Tolerant Post-Quantum Distributed Quorum Signatures},
  author = {Quentin Kniep and Jakub Sliwinski and Roger Wattenhofer},
  journal= {arXiv preprint arXiv:2607.17700},
  year   = {2026}
}