Cryptology ePrint Archive: Report 2019/169

Updatable Anonymous Credentials and Applications to Incentive Systems

Johannes Blömer and Jan Bobolz and Denis Diemert and Fabian Eidens

Abstract: In this paper, we introduce updatable anonymous credential systems (UACS) and use them to construct a new privacy-preserving incentive system. In a UACS, a user holding a credential certifying some attributes can interact with the corresponding issuer to update his attributes. During this, the issuer knows which update function is run, but does not learn the user's previous attributes. Hence the update process preserves anonymity of the user. One example for a class of update functions are additive updates of integer attributes, where the issuer increments an unknown integer attribute value $v$ by some known value $k$. This kind of update is motivated by an application of UACS to incentive systems. Users in an incentive system can anonymously accumulate points, e.g. in a shop at checkout, and spend them later, e.g. for a discount.

In this paper, we (1) formally define UACS and their security, (2) give a generic construction for UACS supporting arbitrary update functions, and (3) construct a practically efficient incentive system using UACS.

Category / Keywords: cryptographic protocols / anonymity, anonymous credentials, incentive systems

Original Publication (with major differences): ACM CCS 2019

Date: received 16 Feb 2019, last revised 18 Oct 2019

Contact author: jbobolz at mail uni-paderborn de, feidens at mail uni-paderborn de

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Note: Full version of conference publication.

Version: 20191018:081740 (All versions of this report)

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