隨著網際網路的快速發展及點對點系統的便利，因此有愈來愈多人使用點對點網路以分享及獲取所需的資源，要如何維護點對點檔案分享系統中使用者的權益，促進每個使用者分享檔案，減少free-riders的問題，需提供足夠的動機誘因。且檔案的品質可能良莠不齊或名不副實，使用者耗費很多資源以下載這些檔案，造成整個網路頻寬的浪費，所以需要有一套措施，選擇信賴的節點以下載檔案。因上述的理由，本研究想要設計兼具下列特性的評價機制：(1)改善檔案內容的正確及品質、(2)選擇可以信賴的節點及(3)提高free-riders對資源的貢獻率。
本研究的評價機制包含四個階段，分別為：(1)檔案的搜尋、(2)選擇適當的節點、(3)檔案的下載及(4)檔案的下載的評分。此評價的機制特點在計算兩部分評分值，即節點對檔案的擁有者評分及系統計算節點所分享資源的評分，前者可以改善節點所分享檔案內容的品質，後者提一獎勵機制以促進節點分享資源，所以可同時改善合理化攻擊中內容的限制及資源的限制問題，而其他改善free-riders問題的相關方案，效用函數、信用系統及代幣的應用可以改善資源的限制問題，使用者的反饋可以改善內容的限制問題，但卻都只有改善一項問題，本研究的評價機制則可同時改善內容的限制以及資源的限制問題，減少free-riders所造成的各項問題。

As the internet is quickly expanded and the peer-to-peer file sharing system is convenient, more and more people use peer-to-peer file sharing systems to get the resources. How to assure rights and interests of users in peer-to-peer file sharing systems, promote every user to share files and reduce the problems of free-riders? To provide enough motivation is the critical factor. Moreover, the quality of files may be uneven. Users have to consume resources to download these files. It will engage the broadland of internet. Therefore we need a way to choose trustworthy peers to download files. Based on above-mentioned, the purpose of this paper is to design a reputation system which has three features, include (1) improving the accuracy and quality of files, (2) choosing trustworthy peers, and (3) increasing the contribution to free-riders.
In this paper, we purpose a four phase reputation system, include (1) searching phase, (2) choosing phase, (3) downloading phase, and (4) evaluating phase. The feature of our system is to compute two portion of reputation scores, such as peer reputation and system reputation. The former can improve the quality of files which are shared by the peers. The latter can stimulate peers to share files. So our reputation system can both improve content restriction and resource restriction in rational attack. But other schemes can only improve one of the restriction. Therefore our reputation system can improve the accuracy and quality of files and increase the contribution to free-riders.

中文參考文獻
1. 李大正，「P2P系統上基於協同式自動信賴對話的信用評等機制」，國立成功大學電腦與通信工程研究所碩士論文，2005年。
2. 高志中，「以DR Signature配合隨機式RSA部分盲簽章所建構之數位內容多受款者付款機制」，國立中央大學資訊管理學系研究所碩士論文，2006年。
英文參考文獻
3. Adar, E. and Huberman, B., “Free riding on gnutella,” http://www.firstmonday.dk/issues/issue5 10/adar, October 2000 (accessed Aug. 2005).
4. Aringhieri, R., Damiani, E. De Capitani Di Vimercati, S., Paraboschi, S. and Samarati, P. “Fuzzy Techniques for Trust and Reputation Management in Anonymous Peer-to-Peer Systems,” Journal of the American Society for Information Science and Technology, Volume 57, Issue 4, Jan 2006, pp:528-537.
5. Buragohain, C., Agrawal, D. and Suri, S., “A game-theoretic framework for incentives in P2P systems,” Proc. of International Conference on Peer-to-Peer Computing, Sep 2003.
6. Chien, E., “Malicious Threats of Peer-to-Peer Networking,” Symantec Security Response, 2003.
7. Cornelli, F., Damiani, E., De Capitani di Vimercati, S., Paraboschi, S. and Samarati, P., “Choosing reputable servents in a P2P network,” Proc. of the Eleventh International World Wide Web Conference, May 2002.
8. Damiani, E., De Capitani di Vimercati, S., Paraboschi, S., Samarati, P. and Violante, F., “A Reputation-Based Approach for Choosing Reliable Resources in Peer-to-Peer Networks,” Proceedings of the 9th ACM conference on Computer and communications security, 2002.
9. Engle, M. and Khan, J. I., “Vulnerabilities of P2P Systems and a Critical look at Their Solutions,” Technical Report, 2006.
10. Fischmann, M. and Gunther, O., “Free riders: Fact or fiction?” Sep 2003.
11. Glance, N. S. and Huberman, B. A., “Dynamics of social dilemmas,” Scientific American, March 1994.
12. Gupta, M., Judge, P. and Ammar, M., “A Reputation System for Peer-to-Peer Networks,” Proceedings of the 13th international workshop on Network and operating systems support for digital audio and video, 2003.
13. Ham, M. and Agha, G.., “ARA: A Robust Audit to Prevent Free-Riding in P2P Networks,” 2005.
14. Huberman, B. A. and Luckose, R., “Social dilemmas and internet congestion,” Science, Volume 277, 1997.
15. Hughes, D., Coulson, G. and Walkerdine, J., “Free riding on gnutella revisited: the Bell Tolls?” IEEE Distributed Systems Online Journal, vol. 6, no. 6, June 2005.
16. Jøsang, A., Ismail, R., and Boyd, C., “A survey of trust and reputation systems for online service provision,” Decision Support Systems, Volume 43, Issue 2, March 2007 pp:618-644.
17. Joseph, S., “NeuroGrid: Semantically Routing Queries in Peer-to-Peer Networks,” International Workshop on Peer-to-Peer Computing, 2002.
18. Joseph, S., “P2P MetaData Search Layers,” Second International Workshop on Agents and Peer-to-Peer Computing, 2003.
19. Jun, S. and Ahamad, M., “Incentives in BitTorrent induce free riding,” Proceeding of the ACM SIGCOMM workshop on Economics of peer-to-peer systems, 2005
20. Liao, W.-C., Papadopoulos, F. and Psounis, K., “A Peer-to-Peer Cooperation Enhancement Scheme and its Performance Analysis,” Journal of Communications, Vol. 1, Issue 7, November 2006.
21. Liao, W.-C., Papadopoulos, F. and Psounis, K., “An efficient algorithm for resource sharing in peer-to-peer networks,” IFIP NETWORKING, Lecture Notes in Computer Science, Vol. 3976, Springer, May 2006, pp:592-605.
22. Lin, Z. and Li, J., “The Online Auction Market in China - A Comparative Study between Taobao and eBay,” Proceedings of the 7th international conference on Electronic commerce, 2005.
23. McFadden, D., “The tragedy of the commons,” Available at http://www.forbes.com/asap/2001/0910/061.html.
24. Parisi, D., “What to do with a surplus,” Simulating Social Phenomenon, 1997, pp:133 – 151.
25. Pretre, B. and Wattenhofer, R., “Attacks on Peer-to-Peer Networks,” 2005.
26. Ramaswanmy, L. and Liu, L., “Free-riding: A new challenge to peer-to-peer file sharing systems,” Proc. of the 36th Hawaii international conference on system sciences, 2003.
27. Saroiu, S., Gummadi, K. and Gribble, S., “A measurement study of peer-to-peer file sharing systems,” Proceedings of Multimedia Computing and Networking, January 2002.
28. Srivatsa, M. and Liu, L., “Vulnerabilities and Security Threats in Structured Peer-to-Peer Systems: A Quantitative Analysis,” Proceedings of the 20th Annual Computer Security Applications Conference, 2004
29. The Gnutella Protocol Specification v0.4 (Document Revision 1.2), http://www9.limewire.com/developer/gnutella_protocol_0.4.pdf, June 2001.
30. Zhou, L., Zhang, L., McSherry, F., Immorlica, N., Costa, M. and Chien, S., “A First Look at Peer-to-Peer Worms: Threats and Defenses,” Peer-to-Peer Systems IV, 4th International Workshop, 2005.
參考網站
31. http://en.wikipedia.org/wiki/P2P
32. http://en.wikipedia.org/wiki/Zipf_distribution
33. http://www.gnutella.com/
34. http://www.kazaa.com
35. http://www.napster.com/
36. http://www.neurogrid.net/twiki/bin/view/Main/PeerToPeerSimulation