[Resource Topic] 2025/430: Non-interactive Anonymous Tokens with Private Metadata Bit

Welcome to the resource topic for 2025/430

Title:
Non-interactive Anonymous Tokens with Private Metadata Bit

Authors: Foteini Baldimtsi, Lucjan Hanzlik, Quan Nguyen, Aayush Yadav

Abstract:

Anonymous tokens with private metadata bit (ATPM) have received increased interest as a method for anonymous client authentication while also embedding trust signals that are only readable by the authority who holds the issuance secret key and nobody else. A drawback of all existing ATPM constructions is that they require client-issuer interaction during the issuance process. In this work, we build the first non-interactive anonymous tokens (NIAT) with private metadata bit, inspired by the recent work of Hanzlik (Eurocrypt '23) on non-interactive blind signatures. We discuss how the non-interaction property during the issuance process allows for more efficient issuance protocols that avoid the need for online signing. We construct an efficient NIAT scheme based on Structure-preserving Signatures on Equivalence Classes (SPS-EQ) and experimentally evaluate its performance. We also present an extension to our NIAT construction that allows the identification of clients who attempt to double-spend (i.e., present the same token twice).

ePrint: https://eprint.iacr.org/2025/430

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