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For the autonomous and selfish features of peers, there are many issues existed in P2P network, such as dynamics of networks, heterogeneity of peers, free-riders, tragedy of commons and malicious behaviors. The topology optimization solutions based on trust are effective methods to solve these problems. However, the trust evaluations in related works only focus on the service trust, or consider both the service trust and the routing trust, but the routing trust evaluation algorithm can not stimulate peers to forward query messages. On this basis, a routing trust evaluation algorithm based on profit sharing is proposed. In the algorithm, according to the contributions of routing recommendation peers, the service demanders share the transaction profit with them in order that the routing recommendation peers can get the routing trust of their neighbors by forwarding query messages. Then, a routing trust aware topology optimization protocol is put forward, which considers both service trust and routing trust. Simulations and analysis show that, the routing trust aware topology optimization protocol can not only promote honest peers to the center of the network, exclude malicious peers and free-riders to the edge of the network, but also improve the query efficiency for honest peers.

The problem of file pollution is prevalent in p2p file sharing system nowadays. The pollution reduces the availability of system sharply. Compared with peer reputation, object reputation is more efficient in face of pollution. Pollution proliferation model based on file object is presented. Vector space similarity is computed to weight the votes collected from other peers. Horting graph-theoretic approach is employed to deal with data sparsity problem. Self-adaptive reputation threshold scheme is adopted to estimate the file authenticity. An anti-pollution p2p file sharing system based on object reputation is established to improve the availability. Simulation results show that the system can distinguish between good and polluted files accurately and thwart the proliferation of pollution in the network with low communication cost. The system can subject freeriders to a penalty and do well in the presence of collusion and bad-mouthing attacks.

Traditional RBAC has trouble in prohibiting cheat and changing roles of users as the amount of users and resources increase, while the trust management can establish trust relationships among entities in grid environment. So the dynamic-role based access control framework assembles both of their merits and simplifies the administration of RBAC. An implementation is deployed in HanHai grid environment.