A Trust Based Assess Control Framework for P2P File-Sharing System

1. A Trust Based Assess Control Framework for P2P File-Sharing System Speaker：Jia-Hui Huang Adviser : Kai-Wei Ke Date ：2004 / 3 / 15

2. Outline • Introduction • Access Control Framework • Search techniques • Conclusion • Reference

3. Introduction • P2P Concept • P2P file sharing allows users on the edge of network to directly access files from on another’s drives. • Why P2P so attractive ? • Provide a flexible and universal model for the exchange of information. • Success of P2P file sharing network (i.e. Gnutella, Napster.....) • But most P2P file sharing no provide access control.

4. Outline • Introduction • Access Control Framework • Search techniques • Conclusion • Reference

5. Requirement • Access control model requirements • No centralized control or support • Peer classification • Encourage sharing files • Limit spreading of malicious and harmful digital content

6. Basic idea of Framework • An access control framework based on the discretionary access control. • Each file being assigned two threshold which capture two access aspects. • Two threshold values • Trust • Contribution

7. Overall Architecture • RD：Resource Discovery • FT：File Transfer • AC：Access Control

8. Authentication • In this framework, a peer is equipped with a 128-bit GUID number and a pair of public/private keys. • Authentication procedure • Client sends authentication request. • Host checks in its database. • Host carries out authentication protocol. • Authentication protocol based on SSL.

9. Scoring system • Host peer needs to classify its client peers. • Client peer is required to supply its rating certificates for the host. • Access values are evaluated via four types of scores • Direct trust • Indirect trust • Direct contribution • Indirect contribution

10. Direct trust • The host’s belief on the client’s capacities, honesty and reliability based on the host’s direct experiences. • In this model, use Bethetal’s formula denotes the trust value that peer i has in peer j

11. Direct trust ( Cont. ) n is the number of peer i’s satisfied transactionswith peer j. is the learning rate – a real number in the interval [0,1] must chose high enough.

12. Indirect trust • Host peer often encounters a client peer that it has never met. • The host’s belief on the client’s capacities, honesty and reliability based on recommendations from other peers.

13. Indirect trust ( Cont. ) • The indirect trust calculated as denotes the indirect trust of peer i in peer j k is a number fixed by the host. will be range 0 to 1 and less than or

14. Indirect trust ( Cont. ) • Indirect trust calculate example assume k = 1

15. Indirect trust ( Cont. ) • The two main reasons why divide by k ? • Avoid the client submit only one highest recommendation. • Allowing the host to specify a required number of recommending peers.

16. Direct contribution • The contribution of the client to the host in term of information download/upload between them. • The direct contribution calculated as is the direct contribution of peer j to peer I denotes the amount information i download from j denotes the amount information j download from i

17. Indirect contribution • The contribution of the client to the network in term of information volume exchange. denotes the indirect contribution of peer j from peer i’s point of view.

18. Granting access ( Cont. ) • The client’s overall trust and contribution values calculated as • value depending on host’s control policy.

19. Granting access • Before making a file available for sharing, a host peer defines two thresholds value for the file. • Any client peer who has equal to or greater than the corresponding thresholds can access the file

20. Trust and contribution management • After completing a download operation, client peer has to issue the host peer a rating certificate. • Rating certificate contains the direct trust and direct contribution value based on the transaction’s satisfaction level.

21. Rating certificate • Rating certificate format

22. Satisfaction level • Evaluate satisfaction level based on the download speeds and file quality. • Five levels of satisfaction • Good • Fair T unchanged • Poor • Corrupted • Unknown • Harmful or malicious add to the black list

23. Local file system • In local storage it stores follow • Received certificates in which the peer itself is the recommended peer. • Certificates which the peer issued to other peers. • A black list of peers who it believes to have committed malicious acts.

24. Framework interaction procedure

25. Outline • Introduction • Access Control Framework • Search techniques • Conclusion • Reference

26. Metrics • Some metrics for evaluate the effectiveness of search technique. • Cost • Bandwidth consumed over every edge in the network on behalf of each query. • Processing cost processing power consumed at every node on behalf of each query.

27. Metrics • Quality of results • Satisfaction of query user specify a value Z, if the number of result is equal or more than Z, the query is satisfied. • Time to satisfaction the time of result arrive.

28. Search techniques • Inefficiency search • blind search (BFS) • Three efficient search techniques： • Iterative deepening • Directed BFS • Local indices

29. Blind search • Node forward to all their neighbors • Find max number of results • But inefficiency

30. Iterative deepening • Satisfaction is the metric of chose. • Multiple breadth-fist searches are initiated with successively larger depth limits until query is satisfied or max depth reached. • Time cost smaller than blind search

31. Iterative deepening • ex. if policy is • Source node initiates a BFS of depth a. • When depth reach, if query not satisfied then continue to depth b and c

32. Directed BFS • Minimizing response time. • DBFS technique send query messages to just a subset of its neighbors. • In order to intelligently select neighbors, node will maintain statistic on its neighbors.

33. Directed BFS • Some heuristic can help us to select the best neighbors • Highest number of results for previous query. • Response messages taken the lowest average hop. • Has forwarded the largest number of messages. • Shortest message queue.

34. Local indices • Maintaining a high satisfaction rate and number of results while keeping low costs. • Node maintains an index over the data of each node within r hops of itself. • Parameter r is adjustable and independent of total size of network. • It must notify when host joint network • Node index the leaving node’s collective will remove after a timeout.

35. Local indices ex. if policy is • Query source will send the query message out to all its neighbors at depth 1. • All node at depth will process and forward to depth 2. • Depth not in list, it forward directly. • Process continue to depth 5

36. Outline • Introduction • Access Control Framework • Search techniques • Conclusion • Reference

37. Conclusion The framework satisfies the requirements of access control for P2P file-sharing system by trust and contribution model, and the implemented contribution work effectively as a payment scheme that giving incentive for users to share their resource. The disadvantage is some overheads in validity of signatures in the rating certificate.

38. Reference • B. Yang and H. Carcia-Molina. Efficient Search in peer-to-peer Networks, ICDCS 2002, Jul 2002 • Thomas Beth and Malte Borcherding and Birgit klein Valuation of trust in open network