A Review of Techniques to Mitigate Sybil Attacks
  Any decentralised distributed network is particularly vulnerable to the Sybil attack wherein a malicious node masquerades as several different nodes, called Sybil nodes, simultaneously in an attempt to disrupt the proper functioning of the network. Such attacks may cause damage on a fairly large scale especially since they are difficult to detect and there has been no universally accepted scheme to counter them as yet. In this paper, we discuss the different kinds of Sybil attacks including those occurring in peer-to-peer reputation systems, self-organising networks and even social network systems. In addition, various methods that have been suggested over time to decrease or eliminate their risk completely are also analysed along with their modus operandi. 
Nitish Balachandran, Sugata Sanyal
cs.CR