Fair Security Protocols with off-line TTP

A fair e-commence protocol can help the Value-Added Service Provider(VASP) and users deal with the exchange safely and efficiently. In this paper, we firstly analyze a PPV(Pay-Per-View) protocol, and find some potential shortcomings and limitations. By multiplying the HASH chains technology, we employ a couple of HASH chains as billing cell, and improve the fairness problem which a cell's loss existed when communication interrupted. Consequently, we propose a new protocol. We assume that user, VASP and mobile network operators communicate each other with an agreed session key. This protocol is able to achieve the service application and payment function commendably. The protocol is specially fit for mobile communication network environment(ad-hoc) as the low computing and storing requirement in mobile terminals,. By systematic research, the protocol not only satisfies the fairness, non-repudiation and security, but also is simply and efficient, so it is a commendable mobile payment protocol.