Paper 2026/433

Round-Optimal Threshold Blind Signatures without Random Oracles

Fabian Regen, TU Wien

Hoeteck Wee, NTT Research

Abstract

This paper presents the first round-optimal threshold blind signature without random oracles. Our construction achieves security in the algebraic group model (AGM) for asymmetric pairing groups, and tolerates adaptive corruption of up to $t-1$ signers, where $t$ is the threshold. We improve upon the recent threshold blind signatures of Lehmann, Nazarian and Özbay (EUROCRYPT 2025) and Jarecki and Nazarian (ASIACRYPT 2025) in two ways: we eliminate both the reliance on random oracles and the need for $q$-type assumptions in the AGM. As a core building block, we introduce a new pairing-based round-optimal blind signature without random oracles, based on the $2$-DL assumption in the AGM. Both blind signature schemes achieve communication and computation costs only twice that of the celebrated blind BLS signature.

@misc{cryptoeprint:2026/433,
      author = {Georg Fuchsbauer and Fabian Regen and Hoeteck Wee},
      title = {Round-Optimal Threshold Blind Signatures without Random Oracles},
      howpublished = {Cryptology {ePrint} Archive, Paper 2026/433},
      year = {2026},
      url = {https://eprint.iacr.org/2026/433}
}