CHEMAS: Identify suspect nodes in selective forwarding attacks

Selective forwarding attacks may corrupt some mission-critical applications such as military surveillance and forest fire monitoring in wireless sensor networks. In such attacks, most of the time malicious nodes behave like normal nodes but will from time to time selectively drop sensitive packets, such as a packet reporting the movement of the opposing forces, and thereby make it harder to detect their malicious nature. In this paper, we propose CHEMAS (CHEckpoint-based Multi-hop Acknowledgement Scheme), a lightweight security scheme for detecting selective forwarding attacks. Our scheme can randomly select part of intermediate nodes along a forwarding path as checkpoint nodes which are responsible for generating acknowledgements for each packet received. The strategy of random-checkpoint-selection significantly increases the resilience against attacks because it prevents a proportion of the sensor nodes from becoming the targets of attempts to compromise them. In our scheme, each intermediate node in a forwarding path, if it does not receive enough acknowledgements from the downstream checkpoint nodes, has the potential to detect abnormal packet loss and identify suspect nodes. We explore the feasibility of our detection scheme using both theoretical analysis and simulations. The simulation results show that our scheme can achieve a high detection rate, even in harsh radio conditions. The communication overhead incurred by our scheme is also within reasonable bounds.