e-coupons: An Efficient, Secure and Delegable Micro-Payment System

In this paper, we propose a new efficient and secure micro-payment scheme, named e-coupons, which can provide the users the facility of delegating their spending capability to other users or their own devices like Laptop, PDA, Mobile Phone, and such service access points. The scheme has the promise of becoming an enabler for various Internet-based services involving unit-wise payment. It gives flexibility to the users to manage their spending capability across various access points for a particular service without obtaining an authorization for each and every access point from a facilitating bank. This flexibility which is not present in the existing micro-payment schemes is essential for accessing ubiquitous e-services and other Internet-based applications. The facility of delegation introduces a slight overhead in respect of the proof or verification of the delegated authorization and security provided to the payments. The payoff from the facility of delegation takes away the burden of the overhead. The paper discusses the design of the protocol and provides a basic analysis of the performance of the system. e-coupons is based on PayWord, a single-seed one-way hash chain for unit-wise payment, TESLA for payment security and SPKI/SDSI as underlying PKI framework for its unique delegation feature. The results obtained from the implementation of e-coupons are quite acceptable and show near real-time response. Our scheme uses multi-seed one-way hash chains for unit-wise payment. Furthermore, it allows an ordered transfer of the portions of payment chains to others. Because of this user's spending capability can be used from different service access points to access the subscribed service, concurrently.