Cryptology ePrint Archive: Report 2021/1680

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

Aisling Connolly and Pascal Lafourcade and Octavio Perez Kempner

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 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.

Category / Keywords: public-key cryptography / Anonymous credentials, Mercurial signatures, SPS-EQ

Original Publication (with major differences): IACR-PKC-2022

Date: received 22 Dec 2021

Contact author: octavio perez kempner at ens fr, aislingmconnolly at gmail com

Available format(s): PDF | BibTeX Citation

Version: 20211222:174210 (All versions of this report)

Short URL: ia.cr/2021/1680


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