Round-Optimal Threshold Blind Signatures Without Random Oracles

Abstract

We present 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 moreover improve on recent threshold blind signatures of Lehmann, Nazarian and Özbay (EUROCRYPT 2025) and Jarecki and Nazarian (ASIACRYPT 2025) by eliminating interactive assumptions and on Reichle and Reinke’s result (PKC 2026) in terms of communication complexity. 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 our schemes achieve communication and computation costs only twice that of the celebrated blind BLS signature.