Paper 2026/692

Efficient Partially Blind Signatures from Isogenies

Chunpeng Ge, Shandong University

Xuan Thanh Khuc, University of Wollongong

Willy Susilo, University of Wollongong

Abstract

(Partially) blind signatures are foundational cryptographic primitives that enable privacy-preserving authentication in digital systems. Blind signatures allow a user to obtain a signature on a message without revealing its content, while partially blind signatures permit the controlled inclusion of agreed-upon public information into the signed message. These primitives are central to applications such as electronic voting, anonymous credentials, and digital cash. The first isogeny-based construction of (partially) blind signatures, CSIOtter, were proposed by Katsumata et al. at CRYPTO'23. However, its concurrent security was later broken by Katsumata et al. (CRYPTO'24) and Do et al. (EUROCRYPT'24). These findings imply that CSI-Otter is secure only in sequential settings. Recently, Hanzlik et al. (ASIACRYPT'25) has proposed a novel framework for concurrently secure blind signatures which can be instantiated from isogenies with smaller signature size (but larger public key and secret key size). It is not known yet whether their construction can be extended to partially blind signatures. In this paper, we present a new and efficient construction of partially blind signatures based on isogenies with substantially smaller signature and public key sizes than CSI-Otter. This makes our construction the most compact post-quantum partially blind signature scheme known to date. As similar to CSIOtter, our scheme uses small challenge space resulting in only achieving sequential concurrent security. Our design follows the Abe-Okamoto paradigm in the group action setting, building upon the framework introduced by Tessaro and Zhu (EUROCRYPT'22), whose security is based on the Discrete Logarithm Problem. We rigorously prove the security of our scheme in the Algebraic Group Action Model and the Random Oracle Model, under the hardness assumption of the Group Action Discrete Logarithm Problem.

Note: This is the full accepted version for FC 2026. The final camera-ready version to be published will be much shorter due to space limits.

@misc{cryptoeprint:2026/692,
      author = {Dung Hoang Duong and Chunpeng Ge and Xuan Thanh Khuc and Willy Susilo},
      title = {Efficient Partially Blind Signatures from Isogenies},
      howpublished = {Cryptology {ePrint} Archive, Paper 2026/692},
      year = {2026},
      url = {https://eprint.iacr.org/2026/692}
}