Secure multi-coupons for federated environments: privacy-preserving and customer-friendly

A digital multi-coupon is similar to a paper-based booklet containing k coupons that can be purchased from one vendor and later redeemed at a vendor in exchange for services. Current schemes, offering privacy-protection and strong security properties such as unsplittability of multi-coupons, address business scenarios with a single vendor and multiple customers, and require customers to redeem coupons in some fixed order. In this paper, we propose a multi-coupon scheme for federated environments that preserves the security and privacy properties of existing schemes, as well as their asymptotic communication and computation complexity. We define a generic formal security model and show that our scheme meets the formal requirements of this framework. Moreover, in contrast to previous solutions, we allow customers to redeem their coupons in an arbitrary order.