1. A reputation-based trust management in peer-to-peer network systems Natalia Stakhanova, Sergio Ferrero, Johnny Wong, Ying Cai Department of Computer Science Iowa State University Ames, Iowa, USA

2. Outline Peer-to-peer(P2P) networks overviewPeer-to-peer(P2P) networks overview Related workRelated work Proposed approachProposed approach ExperimentsExperiments

3. Peer-to-peer (P2P) networks overview P2P network - an overlay network of peers exchanging resourcesP2P network - an overlay network of peers exchanging resources common uses: file sharing, distributed computing, instant messagingcommon uses: file sharing, distributed computing, instant messaging types:types: Centralized (Napster)Centralized (Napster) Central indexing server contains information about all peer’s shared filesCentral indexing server contains information about all peer’s shared files Decentralized (Gnutella, Freenet)Decentralized (Gnutella, Freenet) No central indexing, all peers are equalNo central indexing, all peers are equal Very popularVery popular Hybrid (KaZaA, FastTrack)Hybrid (KaZaA, FastTrack) Supernodes maintain index of files shared by their local peersSupernodes maintain index of files shared by their local peers

4. P2P networks overview Differences with traditional networksDifferences with traditional networks Highly dynamicHighly dynamic autonomous peersautonomous peers peers leave & join the network at any timepeers leave & join the network at any time shared storageshared storage Peers act as servers and clientsPeers act as servers and clients

5. P2P security threats Denial-Of-Service attacks (DoS)Denial-Of-Service attacks (DoS) Decentralized P2P networks (Gnutella)Decentralized P2P networks (Gnutella) Virus distributionVirus distribution Dishonest uploadDishonest upload Unauthorized access to informationUnauthorized access to information Goal: communication with trusted peers only

6. Reputation-based approach Natural mechanism for selecting trusted partners for communicationNatural mechanism for selecting trusted partners for communication limit communication with unreliable peerslimit communication with unreliable peers Most commonly usedMost commonly used

7. Related work Centralized approachesCentralized approaches Debit-Credit Reputation Computation (DCRC) schemaDebit-Credit Reputation Computation (DCRC) schema Each peer tracks its own positive contribution using credit-debit mechanismEach peer tracks its own positive contribution using credit-debit mechanism Reputation Computation Agent (RCA) periodically collects reputationsReputation Computation Agent (RCA) periodically collects reputations Decentralized approachesDecentralized approaches NICENICE Reputation is in form of cookies which express peer’s satisfaction about the transactionsReputation is in form of cookies which express peer’s satisfaction about the transactions If no cookie is found information is requested fromIf no cookie is found information is requested from P2PRepP2PRep Reputation of the peer is based on other peer’s opinionReputation of the peer is based on other peer’s opinion Request peer’s opinion on one’s reputation through polling protocolRequest peer’s opinion on one’s reputation through polling protocol OthersOthers Daswani and Garcia-Molina ’ s schema for allocating resources fairlyDaswani and Garcia-Molina ’ s schema for allocating resources fairly Traffic management based on load-balancing policiesTraffic management based on load-balancing policies DoS attacks onlyDoS attacks only

8. Factors to be considered in reputation-based approach Extensive traffic in Gnutella-like P2P networkExtensive traffic in Gnutella-like P2P network StorageStorage centralcentral locallocal Cooperation of other peersCooperation of other peers System overheadSystem overhead

9. Proposed approach Reputation calculation is based the monitored activity of the connected peersReputation calculation is based the monitored activity of the connected peers assessing the reputation of the peers before accepting traffic from other peersassessing the reputation of the peers before accepting traffic from other peers if traffic is accepted update reputation of peers involvedif traffic is accepted update reputation of peers involved Decentralized - reputations are stored and managed locallyDecentralized - reputations are stored and managed locally

10. Contribution of our approach Fully decentralized modelFully decentralized model Requires no cooperation for reputation computationRequires no cooperation for reputation computation On demand calculationsOn demand calculations Lightweight – little system overheadLightweight – little system overhead

11. Reputation calculation Peer’s reputation indicates its contribution to the functioning of the P2P networkPeer’s reputation indicates its contribution to the functioning of the P2P network Four factors determining reputation:Four factors determining reputation: Resource searchResource search Resource uploadResource upload Resource downloadResource download Traffic extensivenessTraffic extensiveness Factors = actionsFactors = actions Bad actionsBad actions Good actionsGood actions

12. Resource search willingness of a peer to forward trafficwillingness of a peer to forward traffic employ “ trailer ” as an addition to Query message each peer that forwards the query adds its ID to the “ trailer ”each peer that forwards the query adds its ID to the “ trailer ” when peer forms QueryHit, it transfers a “ trailer ” from Query to QueryHitwhen peer forms QueryHit, it transfers a “ trailer ” from Query to QueryHit peer originated a query receives QueryHit with “ trailer ” and updates reputationspeer originated a query receives QueryHit with “ trailer ” and updates reputations

13. Resource upload Indicates another peer ’ s interest in the shared resourceIndicates another peer ’ s interest in the shared resource Completely uploaded file is a successful upload or good actionCompletely uploaded file is a successful upload or good action

14. Resource download reflects the quality of the downloaded informationreflects the quality of the downloaded information User decides if download was successfulUser decides if download was successful

15. Traffic extensiveness help to evaluate the traffic load coming from all connected peershelp to evaluate the traffic load coming from all connected peers based on the average loadbased on the average load load is extensive if it exceeds the average amount by a user pre-defined thresholdload is extensive if it exceeds the average amount by a user pre-defined threshold n L cK > ∑ l j /n * t j=1 L cK - current load from peer k t - threshold n - number of connected peers l j - number of bytes sent by peer j

16. Reputation calculation Reputation value (trust score) is a percent of bad actions happened during a period of timeReputation value (trust score) is a percent of bad actions happened during a period of time R i = BA i / TA i R i - trust score of peer i TA i - total number of considered actions for this peer i BA i - number of bad actions for this peer i

17. Trust thresholds indicate peer ’ s trust policyindicate peer ’ s trust policy percent of bad actions acceptable by the peerpercent of bad actions acceptable by the peer Trust Threshold MeaningDescription Greater than x 1 Distrust Peer is completely untrustworthy. Between x 1 and x 2 Average Peer is trustworthy. Less than x 2 Full trust Peer has a complete trust.

18. The correspondence between trust thresholds and trust score Example: trust score falls in range of “ average ”trust score falls in range of “ average ” -> x 1 – (R i – x 2 ) Computations: 30-(13-4) = 21 21% of peer ’ s traffic is accepted within period k. Given : R i =13 x 1 =30 x 2 =4 R i => x 1 x 1 > R i > x 2 R i =< x 2 No traffic is accepted x 1 –(R i –x 2 ) percent of the traffic from peer i is accepted for a period of time k. All traffic is accepted

19. Experiments: system design P2P client … Security Manager Reputation Manager Reputation repository Internet Connection Engine implementation were based on Phex version 0.9.5.54, a java-based Gnutella client

20. Experimental setup Network : 3 P2P clients set up as UltrapeersNetwork : 3 P2P clients set up as Ultrapeers peer capacity - 20 queries per time period kpeer capacity - 20 queries per time period k k=5 seck=5 sec Extensive traffic threshold t=1.7Extensive traffic threshold t=1.7 Trust thresholdsTrust thresholds x 1 =20x 1 =20 x 2 =5x 2 =5 Initial reputation values for peers were set up manuallyInitial reputation values for peers were set up manually

21. Scenario 1 Decrease of full reputation when peer P1 starts “ acting ” maliciouslyDecrease of full reputation when peer P1 starts “ acting ” maliciously

22. Scenario 2 Reputation gain when peer starts “ acting ” properlyReputation gain when peer starts “ acting ” properly

23. Conclusion We have proposed reputation-based trust management model for P2P networksWe have proposed reputation-based trust management model for P2P networks approach is decentralizedapproach is decentralized requires no peers ’ cooperationrequires no peers ’ cooperation employs only on-demand calculationsemploys only on-demand calculations

24. Future work Enhancement of the model throughEnhancement of the model through user profiling techniquesuser profiling techniques anomaly detectionanomaly detection