The EigenTrust Algorithm for Reputation Management in P2P Networks

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The EigenTrust Algorithm for Reputation
Management in P2P Networks

• Sepandar D.Kamvar Mario T.Schlosser
  Hector Garcia-Molina

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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

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How to Aggregate Local Trust Values?

• Aggregates the ratings of only a few peers
• Cant get a wide view about a peers reputation
• Aggregates the ratings of all the peers
• Congesting the network with system messages
  asking for each peers local trust values at
  every query
• Global Trust Value
• The overall estimation of , for each peer j
• How to calculate these global trust values?

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Aggregating Local Trust Values

• Normalizing Local Trust Values
• Why
  normalizing?
• Aggregating Local Trust Values (transitive trust)
• A Probabilistic Interpretation

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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)

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Basic EigenTrust

• Assumption including server at this stage
• A server stores all the values and performs
  the computation

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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

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Practical Issues(2)

• Inactive Peers
• What happens if peer i doesn't download from
  anybody else?
• Choose to trust the pre-trusted peers

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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

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Distributed EigenTrust

• Assumption Everyone is honest
• Each peer compute its own global trust value

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Algorithm Complexity

• The algorithm converges fast
• A network of 100 peers after 100 query cycles

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Algorithm Complexity(2)

• Specifically limit the number of local trust
  values that a peer reports

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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?

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Assign Score Managers

• DHT (Distributed Hash Table)

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The Algorithm
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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

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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

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Isolating Malicious Peers
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Conclusion

• Goal minimize the impact of malicious peers on
  the P2P system
• Using global trust value
• Compute in a distributed manner