1. The EigenTrust Algorithm for Reputation Management in P2P Networks Sepandar D.Kamvar Mario T.Schlosser Hector Garcia-Molina

2. P2P Networks and Reputation Systems P2P Networks –open and anonymous Problem –Malicious peers –Inauthentic files Reputation Systems –Centralized system (eBay) –Distributed System Local Trust Value j i

3. How to Aggregate Local Trust Values? Aggregates the ratings of only a few peers –Can’t get a wide view about a peer’s reputation Aggregates the ratings of all the peers –Congesting the network with system messages asking for each peer’s local trust values at every query Global Trust Value –The overall estimation of, for each peer j –How to calculate these global trust values?

4. Aggregating Local Trust Values Normalizing Local Trust Values Why normalizing? Aggregating Local Trust Values (transitive trust) A Probabilistic Interpretation i j k

5. Aggregating Local Trust Values (2) The global trust vector; also, the Eigenvector of C The global trust value of peer j (quantify how much trust the system as a whole places peer j)

6. Basic EigenTrust Assumption: including server at this stage –A server stores all the values and performs the computation

7. Practical Issues A priori notions of trust –Can we assign any profit to newcomers? –Only the first few peers to join the network are known to be trustworthy – if, and otherwise –Use instead of

8. Practical Issues(2) Inactive Peers –What happens if peer i doesn't download from anybody else? –Choose to trust the pre-trusted peers

9. Practical Issues(3) Malicious Collectives –a group of malicious peers who know each other –How to prevent them from subverting the system? –The modified algorithm:

10. Distributed EigenTrust Assumption: Everyone is honest Each peer compute its own global trust value:

11. Algorithm Complexity The algorithm converges fast –A network of 100 peers after 100 query cycles

12. Algorithm Complexity(2) Specifically limit the number of local trust values that a peer reports

13. Secure Eigentrust Malicious peers can report false trust values, subverting the system Have a different peer compute the trust value of a peer The trust value of one peer will be computed by more than one other peer How to assign score mangers?

14. Assign Score Managers DHT (Distributed Hash Table)

15. The Algorithm

16. Using Global Trust Values Have each peer download from the most highly trusted peer who responds to its query Two problems –The most highly trusted peers be overloaded

17. Using Global Trust Values(2) –Does not allow newcomers to build reputation Probabilistically based on the trust values –With a probability of 10%, select a peer j that has a zero trust value –

18. Isolating Malicious Peers

19. Conclusion Goal: minimize the impact of malicious peers on the P2P system Using global trust value Compute in a distributed manner