Friend or Flood? Social prevention of flooding attacks in opportunistic networks

Opportunistic networks enable decentralised and infrastructure-less social networking applications, through the cooperation of peer mobile devices to forward messages on one another's behalf. The decentralised and cooperative nature of these networks, however, introduces potential security threats. For instance, malicious nodes may modify messages, or send many messages in an attempt to drain other nodes' resources and thereby disrupt the network. Such attacks are well-studied for wireless ad hoc networks, but may need reconsideration in disconnected opportunistic networks. In this paper we define a simple flooding attack that can deny service in an opportunistic network. We simulate the attack and demonstrate its efficacy using real-world datasets. We furthermore develop a scheme for mitigating the attack, by using the social relations between nodes. The scheme is lightweight, requires only local knowledge to be stored by each node, and is shown to be effective: for one dataset, the median proportion of time spent offline by nodes was reduced from 42.7% to 6.3%.