Paper 2025/1566

Lattice-based Threshold Blind Signatures

Guilhem Niot, PQShield, Univ Rennes, CNRS, IRISA

Michael Reichle, ETH Zurich

Abstract

Blind signatures are a central tool for privacy-preserving protocols. They allow users to obtain signatures from a signer without the signer seeing the signed message. For instance, it enables electronic cash: signatures correspond to coins which can be issued by the bank in a privacy-preserving manner via blind signing. To mitigate the risk of key compromise, threshold blind signatures allow the distribution of the signing key amongst N parties. While recent works have focused on improving the security of this primitive in the classical setting, no construction is known to date in the post-quantum setting. We present the first construction of a threshold blind signature secure in the post-quantum setting, based on lattices. We prove its security under an interactive variant of the SIS assumption introduced in [Agrawal et al., CCS’22]. Our construction has a reasonable overhead of a factor of roughly 1.4 X to 2.5 X in signature size over comparable non-threshold blind signatures over lattices under heuristic but natural assumptions.

@misc{cryptoeprint:2025/1566,
      author = {Sebastian Faller and Guilhem Niot and Michael Reichle},
      title = {Lattice-based Threshold Blind Signatures},
      howpublished = {Cryptology {ePrint} Archive, Paper 2025/1566},
      year = {2025},
      url = {https://eprint.iacr.org/2025/1566}
}