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Reputation Systems II
Sybil Attack, BlogRank, B2Rank, EigenRumor,
             MailRank, TrustRunk



         Yury Lifshi...
Outline

1   Sybil Attack

2   Ranking Blogs

3   Reputations For Fighting Spam

4   Conclusions



                      ...
1
Sybil Attack




               3 / 22
Sybil Attack

   Graph of trust-weighted edges

   n honest nodes + adversary

   overall trust value on attack edges
   (...
Sybil Attack

   Graph of trust-weighted edges

   n honest nodes + adversary

   overall trust value on attack edges
   (...
Negative Result


 Assume reputation scores remain the same
           under isomorphism.
             Is it sybilproof?

...
Negative Result


 Assume reputation scores remain the same
           under isomorphism.
             Is it sybilproof?

...
Negative Result


 Assume reputation scores remain the same
           under isomorphism.
             Is it sybilproof?

...
Positive Results (1/3)

General form of trust flow reputations:

            r(x) = max           trust(p)
                ...
Positive Results (2/3)

Assumptions:
 1
     Extending path nonincreases the trust(p)
 2
       and trust are monotone to ...
Positive Results (2/3)

Assumptions:
 1
     Extending path nonincreases the trust(p)
 2
       and trust are monotone to ...
Positive Results (3/3)


Under assumptions (1-3) sybil attack does not
increase adversary’s reputation




               ...
Positive Results (3/3)


Under assumptions (1-3) sybil attack does not
increase adversary’s reputation

Under assumptions ...
Positive Results (3/3)


Under assumptions (1-3) sybil attack does not
increase adversary’s reputation

Under assumptions ...
SybilGuard (1/2)


   Assume number of attack edges is
   A = o( n/ log n)

   System is distributed, honest nodes follow
...
SybilGuard (2/2)
   For every node fix a bijective mapping
   from in-edges to out-edges
   Take a walk from t of length at...
SybilGuard (2/2)
   For every node fix a bijective mapping
   from in-edges to out-edges
   Take a walk from t of length at...
2
Ranking Blogs




                11 / 22
Ranking Blogs: Factors

   Entities: blogs, posts, communities,
   comments, brand names, external
   websites

   Frineds...
BlogRank

     Any ideas how to rank blogs?




                                    13 / 22
BlogRank

       Any ideas how to rank blogs?

Why not just PageRank?




                                      13 / 22
BlogRank

        Any ideas how to rank blogs?

Why not just PageRank?
Wait a minute, for which graph?




               ...
BlogRank

        Any ideas how to rank blogs?

Why not just PageRank?
Wait a minute, for which graph? Linked blogs:

   H...
B2Rank
B2Rank(x) = BlogReputation × PostQuality




                                           14 / 22
B2Rank
B2Rank(x) = BlogReputation × PostQuality

BlogReputation is computed in PageRank style
for blogroll graph with one ...
B2Rank
B2Rank(x) = BlogReputation × PostQuality

BlogReputation is computed in PageRank style
for blogroll graph with one ...
EigenRumor (1/2)




Picture from “The EigenRumor Algorithm for Ranking Blogs” paper
                                     ...
EigenRumor (2/2)
Notation:
    ¯: reputation score for posts
    r
    ¯ ¯
    a, h: authority and hub scores for bloggers...
EigenRumor (2/2)
Notation:
    ¯: reputation score for posts
    r
    ¯ ¯
    a, h: authority and hub scores for bloggers...
EigenRumor (2/2)
Notation:
    ¯: reputation score for posts
    r
    ¯ ¯
    a, h: authority and hub scores for bloggers...
3
Reputations For Fighting Spam




                                17 / 22
Combining Two Scores
  Hyperlink graph




                       18 / 22
Combining Two Scores
  Hyperlink graph
  Pre-trusted nodes




                       18 / 22
Combining Two Scores
  Hyperlink graph
  Pre-trusted nodes
  Spam nodes




                       18 / 22
Combining Two Scores
  Hyperlink graph
  Pre-trusted nodes
  Spam nodes
  Reputation propagates in a forward
  manner




...
Combining Two Scores
  Hyperlink graph
  Pre-trusted nodes
  Spam nodes
  Reputation propagates in a forward
  manner
  Sp...
Combining Two Scores
  Hyperlink graph
  Pre-trusted nodes
  Spam nodes
  Reputation propagates in a forward
  manner
  Sp...
Combining Two Scores
  Hyperlink graph
  Pre-trusted nodes
  Spam nodes
  Reputation propagates in a forward
  manner
  Sp...
Combining Two Scores
  Hyperlink graph
  Pre-trusted nodes
  Spam nodes
  Reputation propagates in a forward
  manner
  Sp...
4
Conclusions




              19 / 22
Challenges
  Measurable objectives?
  Model for input data?
  Dynamic aspects of reputations?
  Digg-style ranking?
  Pric...
References
  K. Fujimura, T. Inoue, M. Sugisaki
  The EigenRumor Algorithm for Ranking Blogs

  A. Kritikopoulos, M. Sider...
http://yury.name
http://yury.name/reputation.html
Ongoing project: http://businessconsumer.net




                       ...
http://yury.name
http://yury.name/reputation.html
Ongoing project: http://businessconsumer.net


    Thanks for your atten...
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Transcript of "Reputation Systems II"

  1. 1. Reputation Systems II Sybil Attack, BlogRank, B2Rank, EigenRumor, MailRank, TrustRunk Yury Lifshits Caltech http://yury.name Caltech CMI Seminar March 4, 2008 1 / 22
  2. 2. Outline 1 Sybil Attack 2 Ranking Blogs 3 Reputations For Fighting Spam 4 Conclusions 2 / 22
  3. 3. 1 Sybil Attack 3 / 22
  4. 4. Sybil Attack Graph of trust-weighted edges n honest nodes + adversary overall trust value on attack edges (honest-malicious) is limited 4 / 22
  5. 5. Sybil Attack Graph of trust-weighted edges n honest nodes + adversary overall trust value on attack edges (honest-malicious) is limited Question: whether splitting adversarial node into many is beneficial for acquiring higher reputation (rank)? 4 / 22
  6. 6. Negative Result Assume reputation scores remain the same under isomorphism. Is it sybilproof? 5 / 22
  7. 7. Negative Result Assume reputation scores remain the same under isomorphism. Is it sybilproof? Unfortunately, no. Attack strategy? 5 / 22
  8. 8. Negative Result Assume reputation scores remain the same under isomorphism. Is it sybilproof? Unfortunately, no. Attack strategy? Answer: double the graph. 5 / 22
  9. 9. Positive Results (1/3) General form of trust flow reputations: r(x) = max trust(p) Ptx p∈Ptx Notation: t is pre-trusted node Pxy is a family of disjoint paths from t to x 6 / 22
  10. 10. Positive Results (2/3) Assumptions: 1 Extending path nonincreases the trust(p) 2 and trust are monotone to number of paths and edges values, respectively 3 Splitting a path into two does not increase value 7 / 22
  11. 11. Positive Results (2/3) Assumptions: 1 Extending path nonincreases the trust(p) 2 and trust are monotone to number of paths and edges values, respectively 3 Splitting a path into two does not increase value 4 = max 7 / 22
  12. 12. Positive Results (3/3) Under assumptions (1-3) sybil attack does not increase adversary’s reputation 8 / 22
  13. 13. Positive Results (3/3) Under assumptions (1-3) sybil attack does not increase adversary’s reputation Under assumptions (1-4) sybil attack does not increase adversary’s rank 8 / 22
  14. 14. Positive Results (3/3) Under assumptions (1-3) sybil attack does not increase adversary’s reputation Under assumptions (1-4) sybil attack does not increase adversary’s rank Proof? 8 / 22
  15. 15. SybilGuard (1/2) Assume number of attack edges is A = o( n/ log n) System is distributed, honest nodes follow the same protocol Can an honest node t identify (w.h.p.) 2A + 1 nodes in such a way that at most A of them are powered by adversary? 9 / 22
  16. 16. SybilGuard (2/2) For every node fix a bijective mapping from in-edges to out-edges Take a walk from t of length at most n log n using bijection routing At some point make a random switch, than continue another n log n steps using backwalk routing Report a point. Repeat, until 2A + 1 points are collected 10 / 22
  17. 17. SybilGuard (2/2) For every node fix a bijective mapping from in-edges to out-edges Take a walk from t of length at most n log n using bijection routing At some point make a random switch, than continue another n log n steps using backwalk routing Report a point. Repeat, until 2A + 1 points are collected Claim w.h.p. at most A reported nodes are malicious 10 / 22
  18. 18. 2 Ranking Blogs 11 / 22
  19. 19. Ranking Blogs: Factors Entities: blogs, posts, communities, comments, brand names, external websites Frineds, blogroll, subscriptions, hyperlinks, visitors, clicks, votes Time Tags 12 / 22
  20. 20. BlogRank Any ideas how to rank blogs? 13 / 22
  21. 21. BlogRank Any ideas how to rank blogs? Why not just PageRank? 13 / 22
  22. 22. BlogRank Any ideas how to rank blogs? Why not just PageRank? Wait a minute, for which graph? 13 / 22
  23. 23. BlogRank Any ideas how to rank blogs? Why not just PageRank? Wait a minute, for which graph? Linked blogs: Hyperlinks, blogrolls Common commentors/authors, tags, co-references to news 13 / 22
  24. 24. B2Rank B2Rank(x) = BlogReputation × PostQuality 14 / 22
  25. 25. B2Rank B2Rank(x) = BlogReputation × PostQuality BlogReputation is computed in PageRank style for blogroll graph with one change: Blogroll links are weighted by activity level (frequency of blogging and commenting) 14 / 22
  26. 26. B2Rank B2Rank(x) = BlogReputation × PostQuality BlogReputation is computed in PageRank style for blogroll graph with one change: Blogroll links are weighted by activity level (frequency of blogging and commenting) PostQuality is average for PageRank-style score of blog posts Post-to-post links are weighted by referring post activity and time difference 14 / 22
  27. 27. EigenRumor (1/2) Picture from “The EigenRumor Algorithm for Ranking Blogs” paper 15 / 22
  28. 28. EigenRumor (2/2) Notation: ¯: reputation score for posts r ¯ ¯ a, h: authority and hub scores for bloggers P, E: provision and evaluation matrices 16 / 22
  29. 29. EigenRumor (2/2) Notation: ¯: reputation score for posts r ¯ ¯ a, h: authority and hub scores for bloggers P, E: provision and evaluation matrices ¯ ¯ = αPT a + (1 − α)ET h r ¯ ¯ a = P¯, h = E¯ ¯ r r 16 / 22
  30. 30. EigenRumor (2/2) Notation: ¯: reputation score for posts r ¯ ¯ a, h: authority and hub scores for bloggers P, E: provision and evaluation matrices ¯ ¯ = αPT a + (1 − α)ET h r ¯ ¯ a = P¯, h = E¯ ¯ r r Solution: iterative algorithm for ¯: r T T ¯ = (αP P + (1 − α)E E)¯ r r 16 / 22
  31. 31. 3 Reputations For Fighting Spam 17 / 22
  32. 32. Combining Two Scores Hyperlink graph 18 / 22
  33. 33. Combining Two Scores Hyperlink graph Pre-trusted nodes 18 / 22
  34. 34. Combining Two Scores Hyperlink graph Pre-trusted nodes Spam nodes 18 / 22
  35. 35. Combining Two Scores Hyperlink graph Pre-trusted nodes Spam nodes Reputation propagates in a forward manner 18 / 22
  36. 36. Combining Two Scores Hyperlink graph Pre-trusted nodes Spam nodes Reputation propagates in a forward manner Spam score propagates backwards 18 / 22
  37. 37. Combining Two Scores Hyperlink graph Pre-trusted nodes Spam nodes Reputation propagates in a forward manner Spam score propagates backwards Compute spam scores a-la PageRank 18 / 22
  38. 38. Combining Two Scores Hyperlink graph Pre-trusted nodes Spam nodes Reputation propagates in a forward manner Spam score propagates backwards Compute spam scores a-la PageRank Reweight hyperlink graph and pre-trusted nodes 18 / 22
  39. 39. Combining Two Scores Hyperlink graph Pre-trusted nodes Spam nodes Reputation propagates in a forward manner Spam score propagates backwards Compute spam scores a-la PageRank Reweight hyperlink graph and pre-trusted nodes Compute reputations a-la PageRank 18 / 22
  40. 40. 4 Conclusions 19 / 22
  41. 41. Challenges Measurable objectives? Model for input data? Dynamic aspects of reputations? Digg-style ranking? Price of attack? Ranking in social networks? Ranking in RDF data? Billion dollar question: how to avoid arms race? 20 / 22
  42. 42. References K. Fujimura, T. Inoue, M. Sugisaki The EigenRumor Algorithm for Ranking Blogs A. Kritikopoulos, M. Sideri, I. Varlamis BlogRank: ranking weblogs based on connectivity and similarity features M.A. Tayebi, S.M. Hashemi, A. Mohades B2Rank: An Algorithm for Ranking Blogs Based on Behavioral Features A. Cheng, E. Friedman Sybilproof reputation mechanisms H. Yu, M. Kaminsky, P.B. Gibbons, A, Flaxman SybilGuard: defending against sybil attacks via social networks P.A. Chirita, J. Diederich, W. Nejdl MailRank: using ranking for spam detection Z. Gyongyi, H. Garcia-Molina, J. Pedersen Combating web spam with TrustRank M. Dalal Spam and popularity ratings for combating link spam 21 / 22
  43. 43. http://yury.name http://yury.name/reputation.html Ongoing project: http://businessconsumer.net 22 / 22
  44. 44. http://yury.name http://yury.name/reputation.html Ongoing project: http://businessconsumer.net Thanks for your attention! Questions? 22 / 22
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