Sonja Buchegger, Jean-Yves Le Boudec
In mobile ad-hoc networks nodes need to cooperate to communicate, but there are many reasons for non-cooperation. Saving power or preventing other nodes from obstructing a service are merely selfish reasons for non-cooperation, whereas nodes may also actively and maliciously deny service or divert traffic for all sorts of attacks. However, without an infrastructure to rely on, nodes depend on each other
s cooperation. In game-theoretic terms, this is a dilemma. The dominating strategy for individual nodes is not to cooperate, as cooperation consumes resources and it might result in a disadvantage. But if every node follows that strategy, the outcome is undesirable for everyone as it results in a non functional or entirely absent network. Thus non-cooperation poses a threat on the availability of a mobile ad-hoc network. Our approach is to find the selfish and/or malicious nodes and to isolate them, so that misbehavior will not pay off but result in isolation and thus cannot continue. CONFIDANT is short for Cooperation Of Nodes, Fairness In Dynamic Ad- hoc NeTworks` and detects malicious nodes by means of observation or reports about several types of attacks, thus allowing nodes to route around misbehaved nodes and to isolate them. CONFIDANT components are extentions to a routing protocol such as Dynamic Source Routing (DSR). Nodes have a monitor for observations, reputation records for first-hand and trusted second-hand observations about routing and forwarding behavior of other nodes, trust records to control trust given to received warnings, and a path manager to adapt their behavior according to reputation and to take action against malicious nodes. The term reputation is used to evaluate routing and forwarding behavior according to the network protocol, whereas the term trust is used to evaluate participation in the CONFIDANT meta-protocol. In order to avoid slander in the form of wrong accusations and to evaluate trust dynamically we use bayesian statistics. Cooperation, and thus availability, of mobile ad-hoc networks, is a crucial issue that needs to be addressed as a prerequisite for enabling the wide-spread use of mobile ad-hoc networks and user acceptance.