International Association for Cryptologic Research

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Paper: Improved Constructions of Anonymous Credentials From Structure-Preserving Signatures on Equivalence Classes

Authors:
Aisling Connolly , Worldline Global, Paris, France
Pascal Lafourcade , LIMOS, University Clermont Auvergne, France
Octavio Perez Kempner , DIENS, École normale supérieure, CNRS, PSL University
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Conference: PKC 2022
Abstract: Anonymous attribute-based credentials (ABCs) are a powerful tool allowing users to authenticate while maintaining privacy. When instantiated from structure-preserving signatures on equivalence classes (SPS-EQ) we obtain a controlled form of malleability, and hence increased functionality and privacy for the user. Existing constructions consider equivalence classes on the message space, allowing the joint randomization of credentials and the corresponding signatures on them. In this work, we additionally consider equivalence classes on the signing-key space. In this regard, we obtain a \emph{signer hiding} notion, where the issuing organization is not revealed when a user shows a credential. To achieve this, we instantiate the ABC framework of Fuchsbauer, Hanser, and Slamanig (FHS, Journal of Cryptology '19) with a recent SPS-EQ scheme (ASIACRYPT '19) modified to support a fully adaptive NIZK from the framework of Couteau and Hartmann (CRYPTO '20). We also show how to obtain Mercurial Signatures (CT-RSA, 2019), extending the application of our construction to anonymous delegatable credentials. To further increase functionality and efficiency, we augment the set-commitment scheme of FHS19 to support openings on attribute sets disjoint from those possessed by the user, while integrating a proof of exponentiation to allow for a more efficient verifier. Instantiating in the CRS model, we obtain an efficient credential system, anonymous under malicious organization keys, with increased expressiveness and privacy, proven secure in the standard model.
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BibTeX
@inproceedings{pkc-2022-31712,
  title={Improved Constructions of Anonymous Credentials From Structure-Preserving Signatures on Equivalence Classes},
  publisher={Springer-Verlag},
  author={Aisling Connolly and Pascal Lafourcade and Octavio Perez Kempner},
  year=2022
}