| dc.description.abstract | The peer-to-peer applications are widely used today. In particular, the filesharing
system is a popular application in P2P. The peers in file-sharing system share their resources in P2P overlay network. Actually, Peers will maximize their utility, but they refuse to contribute their resources, because they do not reap the benefits of their contribution. The behavior which a peer does not attempt to share his recourse and gets other’s only is termed “free-riding”. Researchers have proposed some schemes to encourage the peers to share their resources, such as PPay and OFPPay.
PPay and OFPPay provide payment protocols in P2P environment. They claim their protocols are secure and the coin is transferable. However, we find out a weakness of OFPPay and propose an attack on PPay. Then we provide two countermeasures to resist the attack and the weakness, respectively. In terms of broker’s and peers’ workload, our improved schemes are the same as PPay and OFPPay.
Nowadays, the transferable coin has lack of flexibility. In practice, the denomination of coin may not match the price of content, therefore, when a customer pays to a vendor, and the vendor sometimes needs to give change to the customer. It is hard to implement this concept. We propose transferable and divisible coins instead of change. The divisible coins are flexible, and they can be divided into several coins, and these coins are transferable.
PPay relies on online third parties. The communication cost is high and time latency is long. For these reasons, we propose two two-way SVP schemes. The first one is Symmetric-key Based Two-way SVP. It uses a tamper proof device to implement offline payment. And all of the employed security component are lightweight, such as hash and MAC. The other one is Asymmetric-key Based Two-way SVP. It is reliable since all of the devices hold different keys. The system will not crash when a stored key has been compromised.
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