The Sybil Attack, J. R. Douceur, IPTPS 2002. Clifton Forlines CSC2231 Online Social Networks 11/1/2007 Outline • Brief overview of the paper • Discussion on differences between P2P networks and OSN and on how this effects Sybil attacks Sybil Attack • “Sybil” (1973) by Flora Rheta Schreiber • Attacker creates multiple identities to control a large portion of the network and overcome redundancy 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 Identity Validation • Four Lemmas “prove” that Sybil attacks are always possible without centralized authority Lemma 1 • Because entities are heterogeneous in terms of capabilities, a malicious entity can create several “minimal” identities • Lower-bound on number of identities Lemma 2 • Unless identities are tested simultaneously, a compromised entity can create any number of identities • Simultaneous identity verification not practical 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 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. Overview Conclusion • Networks require centralized authority to validate network identities • Without one, Sybil attacks are always a possibility 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? Identity Validation ? Identity Validation Identity Validation • OSN have lots of techniques to validate identities that are not present in P2P Network Network Network What about the links? 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 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 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 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 Links in a Social Network • What does a link in a social network signify? Links in a Social Network • What does a link in a social network signify? – Indicates trust Links in a Social Network • What does a link in a social network signify? – Indicates trust – Vouches for individual Links in a Social Network • How many links can a malicious node in a P2P network create? • How many in an OSN? 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. Network What about the links? Network Network Network Network Network Network • How can we identify this type of edge without global network typology? 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. Other Discussion Topics • IPv6 privacy (mentioned in paper)
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