Cryptology ePrint Archive: Report 2020/072

Efficient Anonymous Tokens with Private Metadata Bit

Ben Kreuter and Tancrede Lepoint and Michele Orrù and Mariana Raykova

Abstract: We present a cryptographic construction for anonymous tokens with private metadata bit, called PMBTokens. This primitive enables an issuer to provide a user with a lightweight, single-use anonymous trust token that can embed a single private bit, which is accessible only to the party who holds the secret authority key and is private with respect to anyone else. Our construction generalizes and extends the functionality of Privacy Pass (PETS’18) with this private metadata bit capability. It is based on the DDH and CTDH assumptions in the random oracle model and provides unforgeability, unlinkability, and privacy for the metadata bit. Both Privacy Pass and PMBTokens rely on non-interactive zero-knowledge proofs (NIZKs). We present new techniques to remove the need for NIZKs, while still achieving unlinkability. We implement our constructions and we report their efficiency costs.

Category / Keywords: cryptographic protocols /

Original Publication (with major differences): CRYPTO 2020

Date: received 23 Jan 2020, last revised 13 Jan 2021

Contact author: benkreuter at google com,tancrede@google com,michele orru@ens fr,marianar@google com

Available format(s): PDF | BibTeX Citation

Note: An abridged version appears in the proceedings of CRYPTO 2020.

Version: 20210113:200918 (All versions of this report)

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