Stalk me if you can: the anatomy of sybil attacks in opportunistic networks

Opportunistic Networks are envisioned to complement infrastruc-ture-based communication in overloaded cellular settings, in remote areas, during and immediately after large scale disasters. On account of their highly distributed and dynamic nature, as well as of their dependence on the honest cooperation of nodes, Opportunistic Networks are particularly vulnerable to sybil attacks. In a sybil attack, a node assumes multiple identities and attempts to form many links to the rest of the network, with the aim of gaining access to resources, influencing the network, circumventing detection of misbehavior ("spread the blame"), etc. Sybil attacks have been studied extensively in the context of distributed systems and online social networks. However, the Opportunistic Networking setting brings new challenges, specific to the network conditions: forming links may require significant resources from the attacker (e.g. time, speed, multiple devices, etc), and each link is ephemeral. In this paper, we study the types and effectiveness of sybil attacks that are possible in Opportunistic Networks, under various resource constraints on the attacker. We evaluate each attack based on the influence the attacker can gain through it. We find that sybil attacks, even with relatively unconstrained resources, are much harder to implement in the Opportunistic Networking setting, due to the link establishment mechanisms using mobility. We believe this is a very important first step towards understanding and defending against sybil attacks in such networks.