Issuer-Hiding Anonymous Tokens and Credentials from Key-Randomizable Signatures

Andrea Flamini; Karla Friedrichs; Jonathan Katz; Watson Ladd; Anja Lehmann; Marek Sefranek

Paper 2026/870

Issuer-Hiding Anonymous Tokens and Credentials from Key-Randomizable Signatures

Andrea Flamini

, Hasso Plattner Institute, University of Potsdam

Karla Friedrichs

, Hasso Plattner Institute, University of Potsdam

Jonathan Katz

, Google (United States)

Watson Ladd

, Akamai (United States)

Anja Lehmann

, Hasso Plattner Institute, University of Potsdam

Marek Sefranek

, TU Wien

Abstract

Anonymous authentication schemes allow a user to prove they have been authorized by some issuer, without revealing any additional information about the user's identity. Two variants are currently seeing strong real-world interest. Anonymous tokens (ATs) allow one-time proofs of authorization, e.g., for privacy-preserving rate limiting as currently being pursued in the MoLE effort at the IETF. Anonymous credentials (ACs) incorporate attributes that can be selectively disclosed in an unbounded number of proofs; these underpin digital-identity systems such as the European Digital Identity (EUDI) wallet. Both anonymous tokens and credentials are envisioned as being deployed in systems with multiple issuers. In standard schemes, proofs reveal which issuer authorized a user, leaking more information than necessary and shrinking a user's anonymity set. To address this, there has been significant recent interest in issuer-hiding schemes that only reveal that the authorizing issuer lies in a specified policy set. We present generic constructions of issuer-hiding ATs/ACs based on key-randomizable signatures that give rise to several efficient instantiations. Specifically, we show efficient issuer-hiding ATs based on the Tessaro–Zhu blind-signature scheme, and efficient issuer-hiding ACs (without policy keys) compatible with existing BBS-based schemes.

Note: This version subsumes and extends an earlier version titled "Issuer-Hiding BBS-Based Anonymous Credentials without Policy Keys".

Metadata

Available format(s): PDF
Category: Cryptographic protocols
Publication info: Preprint.
Keywords: anonymous credentials anonymous tokens issuer hiding BBS signatures
Contact author(s): andrea flamini @ hpi de
karla friedrichs @ hpi de
jkatz2 @ gmail com
watsonbladd @ gmail com
anja lehmann @ hpi de
marek sefranek @ tuwien ac at
History: 2026-10-05: revised; 2026-05-04: received; See all versions
Short URL: https://ia.cr/2026/870
License: CC BY

BibTeX

@misc{cryptoeprint:2026/870,
      author = {Andrea Flamini and Karla Friedrichs and Jonathan Katz and Watson Ladd and Anja Lehmann and Marek Sefranek},
      title = {Issuer-Hiding Anonymous Tokens and Credentials from Key-Randomizable Signatures},
      howpublished = {Cryptology {ePrint} Archive, Paper 2026/870},
      year = {2026},
      url = {https://eprint.iacr.org/2026/870}
}