Efficient E-coupon systems with strong user privacy.

We propose two novel e-coupon systems that can achieve the following new properties: (1) The coupon issuer (or service provider) can trace the identity of a dishonest user while the identity privacy (or anonymity) of a honest user is still well protected. (2) A honest user's redemption privacy (i.e., the items chosen when redeeming an e-coupon) is well protected from the service provider. (3) If a dishonest user redeems an e-coupon for more than the pre-determined number of times, then the user will lose the redemption privacy (i.e., all the choices the user has made in the previous redemptions can be revealed). We first propose a novel blind signature scheme that we employ together with oblivious transfer to construct our first e-coupon system, which achieves the first two properties without the involvement of any trusted third party. Then we propose a novel oblivious transfer scheme and use it to construct the second e-coupon system that can achieve all the properties given above. We also define the formal security models for these new security requirements, and show that our new e-coupon systems are proven secure in the proposed models. [ABSTRACT FROM AUTHOR]