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DSybil: Optimal Sybil-Resistance for Recommendation Systems

DSybil: Optimal Sybil-Resistance for Recommendation Systems. Ennan Zhai Peking University enzhai@pku.edu.cn. What is the Sybil Attack ?. Sybil Nodes. Honest Nodes. How about the Current Work ?. SybilGuard SybilLimit DSybil SumUp Approach using Puzzles.

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DSybil: Optimal Sybil-Resistance for Recommendation Systems

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  1. DSybil: Optimal Sybil-Resistance for Recommendation Systems Ennan Zhai Peking University enzhai@pku.edu.cn

  2. What is the Sybil Attack ? Sybil Nodes Honest Nodes

  3. How about the Current Work ? • SybilGuard • SybilLimit • DSybil • SumUp • Approach using Puzzles

  4. Let’s recall SybilGuard … … • SybilGuard: • Bounds the number of sybil nodes accepted; • Guarantees are with high probability; • Approach: Acceptance based on random route intersection between verifier and suspect.

  5. SybilGuard Basic Insight • Undirected graph • Nodes = identities • Edges = strong trust E.g., colleagues, relatives

  6. sybil nodes SybilGuard Basic Insight Sybil Nodes may collude – the Adversary honest nodes attack edges malicious user

  7. sybil nodes SybilGuard Basic Insight But cannot search for such cut brute-force… honest nodes

  8. Normal Random Walk f a e b d c pick random edge d pick random edge e pick random edge c

  9. Random 1 to 1 mapping between incoming edge and outgoing edge Random Route f a e b d a  d d  e c randomized routing table e  d b  a c  b f  f d  c Using routing table gives Convergence Property: Routes merge if crossing the same edge

  10. Intersection Verifier Suspect Honest Nodes Sybil Nodes

  11. Intersection Verifier Suspect same intersection Sybil Nodes Honest Nodes

  12. Intersection Verifier for a given intersection

  13. The Lack of SybilGuard ? Is SybilGuard so perfect ? What is the lack of the approach ? … … … …

  14. SybilLimit SybilLimit is a novel protocol which leverages the same insight as the SybilGuard but offers dramatically improved and near-optimal guarantees. Based on the large real-world social networks, SybilLimit has been proved by the first evidence that real-world social networks are indeed fast mixing.

  15. How about DSybil ? This work aims to answer the question: Is it possible to sufficiently diminish the influence of ( a potentially unlimited number of ) sybil identities based on historical behavior ?

  16. DSybil’s Contributions ? • Defend against unlimited num of sybil; • The loss is limited; • Work proved the last optimal system; • Provide a growing defense.

  17. DSybil’s Target Scenarios ? • Recommendation Systems: • Credence: recommends content items; • Digg: recommends stories. Votes: A vote claims a certain object to be good, and this is the only kind of vote DSybil uses.

  18. Leveraging Trust The Obvious, the Subtle and the Challenge … …

  19. DSybil • Two Key Algorithms Details: • Assumes the total number of sybil identities is M (Alg-A); • Improves the algorithm so that it can tolerate an unlimited number of sybil identities, as long as the number of sybil voters on any given object is bounded within M (Alg-B).

  20. Design (Alg-A) At Most M Sybil Identities Total

  21. Design (Alg-A) Overwhelming: An object is overwhelming, if the total trust of the identities voting for the object is at least some constant c, where c > S.

  22. Example

  23. Example

  24. Discussions (Alg-A) Some Intuition about the first algorithm of DSybil … …

  25. Guarantees (Alg-A)

  26. Guarantees (Alg-A)

  27. Design (Alg-B) How about M Sybil Voters on each object ?

  28. Design (Alg-B)

  29. Discussions (Alg-B) Some Intuition about the second algorithm of DSybil … …

  30. Guarantees (Alg-B)

  31. Guarantees (Alg-B)

  32. A Growing Defense A salient property of DSybil is that its defense against attacks grows over time. The growing defense comes from 3 factors … …

  33. The Rest of DSybil Some further extensions and deeper look are in the technical report. Loosely Bounding M can also be seen in the paper and report … …

  34. My Discussions • The Sybil Attack; • Defense Mechanisms; • Future Works.

  35. Thanks !

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