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Establishing Pairwise Keys in Wireless Sensor Networks Using Multiple Paths
Hui Ling and Taieb Znati

Wireless networks of low-power sensing devices are becoming a ubiquitous part of the next generation computing and communication landscape. Securing the operations of these networks, in a manner that meets the severe resource constraints of the sensing devices, is challenging. The common perception is that public key cryptography is not suitable for wireless sensor networks, due to its complexity and potentially prohibitive power consumption. To address this shortcoming, symmetric key based encryption schemes have been presented.

Symmetric cryptography in wireless sensor networks often relies on resource-aware, random key predistribution techniques. In most of these schemes, each sensor node is loaded with a key ring before deployment. Neighboring nodes are considered to be connected through a secure link if they share a common key. Nodes which are not directly connected through a secure link, negotiate a symmetric key through a secure path. However, since different symmetric keys are used for different links connecting adjacent nodes along the secure path, each intermediate node must first decrypt the key-carrying message received from the upstream node and encrypt it, using the key shared with the downstream node, before forwarding it toward the destination node. As a result of this process, the negotiated key is revealed to each node along the secure path, thereby weakening the security of the path key establishment process. To address this shortcoming, a novel scheme, referred to as Pairwise Key Establishment using Multi-path (PKEM), is proposed. PKEM uses a selected set of node-disjoint paths to securely negotiate symmetric keys between sensor nodes. We further extend PKEM to (i) Reliable PKEM (R-KEM) to defend against dropping attacks, and (ii) Enhanced PKEM (E-PKEM) to harden the security of path key establishment in wireless sensor networks. The analysis shows that the scheme is highly secure against attacks where a predetermined number of nodes is compromised by an attacker. A simulation-based evaluation confirms the analytical results and shows that the security gain achieved using multi-paths is significant.

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