In a mobile ad hoc network (MANET), a source node must rely on intermediate nodes to forward its packets along multi-hop routes to the destination node. Due to the lack of infrastructure in such networks,secure and reliable packet delivery is diffocult to achieve. We propose a robust cooperative trust establishment scheme to improve the reliability of packet delivery in MANETs, particularly in the presence of malicious nodes. In the proposed scheme, each node determines the trustworthiness of the other nodes with respect to reliable packet forwarding by combining first-hand trust information obtained independently of other nodes and second-hand trust information obtained via recommendations from other nodes. First-hand trust information for neighbor nodes is obtained via direct observations at the MAC layer whereas first-hand information for non-neighbor nodes is obtained via feedback from acknowledgements sent in response to data packets. The proposed scheme exploits information sharing among nodes to accelerate the convergence of trust establishment procedures, yet is robust against the propagation of false trust information by malicious nodes. We present simulation results which demonstrate the effectiveness of the proposed scheme in a variety of scenarios involving nodes that are malicious both with respect to packet forwarding and trust propagation.
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