P2P网络的发展得益于其非中心化、开放性、节点协同合作的特点，但仍然面临许多问题与挑战，搭便车、文件污染问题制约了P2P传输效率；网络攻击严重影响了P2P终端安全性；恶意欺骗导致节点难以建立可靠的信任关系。本论文采取理论分析和机制设计相结合的方式，重点围绕P2P服务可信性评价模型与增强服务可信性的相关安全机制等内容进行研究。论文主要工作包括：（1）结合安全性和系统可信赖性评价模型，从面向服务的角度提出了P2P服务可信性评价模型与指标体系，并从架构可信赖性与资源安全性两方面定义了服务可信性的相关属性及其量化分析方法。针对三种典型的P2P网络结构，从性能、可靠性、容错率和可扩展性等指标进行了深入分析，给出了定量计算公式，并通过仿真实验分析评价指标与P2P网络参数之间的变化关系。（2）提出了基于TNC架构的P2P可信接入控制机制，基于XACML描述语言设计了认证和策略判定机制，保证终端节点可信接入P2P网络，完善了TNC系统在应用层接入控制的功能。同时针对TNC架构，提出了基于半马尔可夫过程的安全量化方法，并设计了改进协议，增强TNC可信接入控制的安全性。（3）针对社会化P2P网络，设计了带有不确定性风险评估和隐私保护的信任管理机制，针对不可信的节点进行风险评估，能够有效激励节点相互合作，与传统的信任机制相比，对于恶意节点的Bad-mouth行为更具有鲁棒性，而且采取角色与信任相结合的控制策略与加密方法，能够允许用户灵活配置访问控制策略，有效的保护用户的个人隐私。（4）为了提高P2P网络的文件可用性和完整性，提出了一套针对BitTorrent网络的快速有效的反文件污染机制，包括基于相同爱好者的版本选择策略和早期污染警报机制。实验表明该机制能有效帮助用户避免选择污染文件的种子，即使节点已经开始下载污染文件，也能及时识别污染，限制污染传播的范围和程度。该机制对于恶意节点的欺骗行为，能有较好的鲁棒性。
Peer-to-Peer technique has achieved remarkable development and widely application, because of its great advantages on distributed data sharing and dynamic peer cooperation. However, there still remain several problems and challenges in P2P research, such as: free-riding problem and content pollution attack seriously impact on P2P efficiency and availability; due to lack of endpoint authentication mechanism, various network attacks threaten P2P security protection; maliciously cheating behaviors impede peers to establish reliable trust relations. The dissertation gives an intensive study on building evaluation model and enhanced mechanisms of service-oriented dependability for P2P networks through theoretical analysis and mechanism design. The work is summarized as follows:（1）We integrate evaluation model and technologies of network security and system dependability, and propose an evlatuion model and attributes of Service-oriented Dependability (SOD) for P2P network from prespective of service-oriented computing system. We give definition and quantitative analysis methods of each attributes of SOD in P2P. And by consideration of three typical P2P network structures (centralized structure, fully distributed structure, hierarchical structure), we provide detailed quantitative analysis on SOD attributes of reliability, performance, fault tolerance and scalability.（2）We propose a novel P2P trusted access control framework based on Trusted Network Connect (TNC), and design mechanisms of peer authentication and policy decision based on XACML in order to protect endpoint security and enrich the access control function in application layer for TNC architecture. Besides this, we make security analysis on interface protocol of TNC and provide security quantitative methods based on SMP, finally we add some protection mechniams on interface protocol according to security analysis.（3）According to research difficulties of social-based P2P network, we design a new trust management solution with uncertainly risk evlaution and privacy preserving. Fot those untrust peers, we bring in risk factor to provide differentiated service to encourage peers cooperating. Comparing with existing trust model, our solution is more robust when facing bad-mouth cheating behaviors. Another advantage is that we build access control mechanism based user role and trust evalution, which allow users to configure their access policy flexibly and protect personal privacy.（4）To improve content availability and integrity of P2P network, we propose a set of anti-pollution scheme for BitTorrent, which includes tastebuddy-based version selection strategy (VSS) and early warning mechanism for pollution awareness (PAM). Simulation results shows that: our method can obviously help users avoid selecting polluted versions and choose high-quality torrent, even when user begin to download polluted content, users can be aware of pollution quickly and restrict the level of pollution dissemination. According to mathematic analysis, it indicates that our scheme still has strong robustness when maliciously cheating behaviors happen.
