CSC2231 - Sybil review

The Sybil Attack
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John R. Douceur

The paper presents security issues, in P2P systems, based on a faulty
entity that presents multiple identities. This kind of attacks are
called Sybil attacks and, without a central trusted authority that can
vouch for each entity, they are possible.

The strength of paper is represented by the clear description of Sybil
attacks. The author shows that theses attacks may happen in any P2P
system that doesn't have a central authority or that doesn's satisfy
the unrealistic assumptions the author states (homogeneity and simultaneous
validation of entities). The author proposes tests based on each node's
resources in order to limit the attack. However, P2P systems are very
heterogenous and a strong node (in terms of storage, processing power,
bandwidth) can act as several weak nodes with minimum acceptable resources.

The problem with a central authority is that this becomes a single point
of failure. There are also scalability issues in wide-area systems.
 
Perhaps the author could have discussed a little bit about why using a
straightforward approach, like IP addresses (though he states CFS), in
identifying entities is not a good solution. This is mainly due to LANs
(behind NATs) sharing a common pool of public IP addresses. Although it
may work in terms of security (by imposing replication to different IPs),
many correct entities may never be used. However, a security problem is
the possibility of someone controlling a large number of IP addresses.
Received on Thu Nov 17 2005 - 10:31:20 EST