A privacy-protecting coupon system

  • Authors:
  • Liqun Chen;Matthias Enzmann;Ahmad-Reza Sadeghi;Markus Schneider;Michael Steiner

  • Affiliations:
  • HP Labs, Bristol, United Kingdom;Institute for Secure Information Technology (SIT), Fraunhofer Gesellschaft (FhG), Darmstadt, Germany;Ruhr-University Bochum, Bochum, Germany;Institute for Secure Information Technology (SIT), Fraunhofer Gesellschaft (FhG), Darmstadt, Germany;IBM T.J. Watson Research Center, Yorktown Heights, NY

  • Venue:
  • FC'05 Proceedings of the 9th international conference on Financial Cryptography and Data Security
  • Year:
  • 2005

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Abstract

A coupon represents the right to claim some service which is typically offered by vendors. In practice, issuing bundled multi-coupons is more efficient than issuing single coupons separately. The diversity of interests of the parties involved in a coupon system demands additional security properties beyond the common requirements (e.g., unforgeability). Customers wish to preserve their privacy when using the multi-coupon bundle and to prevent vendors from profiling. Vendors are interested in establishing a long-term customer relationship and not to subsidise one-time customers, since coupons are cheaper than the regular price. We propose a secure multi-coupon system that allows users to redeem a predefined number of single coupons from the same multi-coupon. The system provides unlinkability and also hides the number of remaining coupons of a multi-coupon from the vendor. A method used in the coupon system might be of independent interest. It proves knowledge of a signature on a message tuple of which a single message can be revealed while the remaining elements of the tuple, the index of the revealed message, as well as the signature remain hidden.