Paper 2025/483

Adaptively Secure Threshold Blind BLS Signatures and Threshold Oblivious PRF

Stanislaw Jarecki, University of California, Irvine
Phillip Nazarian, University of California, Irvine
Abstract

We show the first threshold blind signature scheme and threshold Oblivious PRF (OPRF) scheme which remain secure in the presence of an adaptive adversary, who can adaptively decide which parties to corrupt throughout the lifetime of the scheme. Moreover, our adaptively secure schemes preserve the minimal round complexity and add only a small computational overhead over prior solutions that offered security only for a much less realistic static adversary, who must choose the subset of corrupted parties before initializing the protocol. Our threshold blind signature scheme computes standard BLS signatures while our threshold OPRF computes a very efficient "2HashDH" OPRF [JKK14]. We prove adaptive security of both schemes in the Algebraic Group Model (AGM). Our adaptively secure threshold schemes are as practical as the underlying standard single-server BLS blind signature and 2HashDH OPRF, and they can be used to add cryptographic fault-tolerance and decentralize trust in any system that relies on blind signatures, like anonymous credentials and e-cash, or on OPRF, like the OPAQUE password authentication and the Privacy Pass anonymous authentication scheme, among many others.

Metadata
Available format(s)
PDF
Category
Cryptographic protocols
Publication info
Preprint.
Contact author(s)
stanislawjarecki @ gmail com
pnazaria @ uci edu
History
2025-03-14: approved
2025-03-14: received
See all versions
Short URL
https://ia.cr/2025/483
License
Creative Commons Attribution
CC BY

BibTeX

@misc{cryptoeprint:2025/483,
      author = {Stanislaw Jarecki and Phillip Nazarian},
      title = {Adaptively Secure Threshold Blind {BLS} Signatures and Threshold Oblivious {PRF}},
      howpublished = {Cryptology {ePrint} Archive, Paper 2025/483},
      year = {2025},
      url = {https://eprint.iacr.org/2025/483}
}
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