Byzantine Fault-Tolerant Post-Quantum Distributed Quorum Signatures

2026-07-20

AI Summary

This work addresses the challenge that existing post-quantum group signature schemes struggle to simultaneously achieve constant-size signatures and efficient aggregation, hindering the migration of Byzantine fault-tolerant systems to post-quantum security. To overcome this limitation, the paper introduces a novel paradigm—distributed quantum-safe signatures (DQS)—which, without relying on new cryptographic primitives, combines standard post-quantum digital signatures with Bracha’s reliable broadcast protocol. By treating certificate construction as a local event and decoupling safety from liveness guarantees, the proposed mechanism achieves constant-size messages and quadratic communication complexity. Consequently, its communication overhead in large-scale systems matches that of classical BLS-based schemes and significantly outperforms existing post-quantum group signature constructions.

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.

Problem

• Byzantine Fault Tolerance
• Post-Quantum Cryptography
• Quorum Signatures
• Distributed Signatures
• Constant-Size Certificates

Innovation

• Distributed Quorum Signature
• Post-Quantum Cryptography
• Byzantine Fault Tolerance
• Constant-Size Messages
• Approval Broadcast