1. The Sybil Attack, J. R. Douceur, IPTPS 2002. Clifton Forlines CSC2231 Online Social Networks 11/1/2007

2. Outline Brief overview of the paper Discussion on differences between P2P networks and OSN and on how this effects Sybil attacks

3. Sybil Attack “Sybil” (1973) by Flora Rheta Schreiber Attacker creates multiple identities to control a large portion of the network and overcome redundancy

4. Identity Validation How does an entity know that two identities come from different entities? Centralized server is one option Douceur mentions three mechanisms of testing independence of identities in P2P –Communication –Computation –Storage

5. Identity Validation Four Lemmas “prove” that Sybil attacks are always possible without centralized authority

6. Lemma 1 Because entities are heterogeneous in terms of capabilities, a malicious entity can create several “minimal” identities Lower-bound on number of identities

7. Lemma 2 Unless identities are tested simultaneously, a compromised entity can create any number of identities Simultaneous identity verification not practical

8. Lemma 3 If a certain number of identities must vouch for a new identity for it to be accepted, then a set of compromised identities can create any number of new fake identities

9. Lemma 4 Without simultaneous validation of identities by a set of trusted entities, a single faulty entity can present many identities. Again, simultaneous validation is difficult in real-world networks.

10. Overview Conclusion Networks require centralized authority to validate network identities Without one, Sybil attacks are always a possibility

11. Identity Validation in an OSN Douceur mentions three mechanisms of testing independence of identities in P2P –Communication –Computation –Storage What mechanisms exist for social networks?

12. Identity Validation ?

14. OSN have lots of techniques to validate identities that are not present in P2P

15. Network

17. What about the links?

18. Links in a Social Network What are the Differences between links in a P2P network and links in an on-line social network?

19. Links in a Social Network What are the Differences between links in a P2P network and links in an on-line social network? –Links in OSN correspond to real-world links

20. Links in a Social Network What are the Differences between links in a P2P network and links in an on-line social network? –Links in OSN correspond to real-world links –Links in OSN take time and effort to setup

21. Links in a Social Network What are the Differences between links in a P2P network and links in an on-line social network? –Links in OSN correspond to real-world links –Links in OSN take time and effort to setup –Links in OSN cluster and have high # of intra-cluster connections

22. Links in a Social Network What does a link in a social network signify?

23. Links in a Social Network What does a link in a social network signify? –Indicates trust

24. Links in a Social Network What does a link in a social network signify? –Indicates trust –Vouches for individual

25. Links in a Social Network How many links can a malicious node in a P2P network create? How many in an OSN?

26. Links in a Social Network How many links can a malicious entity in a P2P network create? –As many as one wants. (mostly) How many in an OSN? –As many as one has time and effort to create.

27. Network What about the links?

28. Network

33. How can we identify this type of edge without global network typology?

34. Summary OSN have lots of techniques to validate identities that are not present in P2P Links in an OSN –Indicates trust –Vouches for individual –correspond to real-world links –take time and effort to setup –cluster and have high # of intra-cluster connections Malicious entity can only create as many links as they have time and effort to create.

35. Other Discussion Topics IPv6 privacy (mentioned in paper)