23. Key Management in Sensor Networks

Secure communications in wireless ad hoc networks require setting up end-to-end secret keys for communicating node pairs. It is widely believed that although being more complex, a probabilistic key predistribution scheme is much more resilient against node capture than a deterministic one in lightweight wireless ad hoc networks. Supported by the surprisingly large successful attack probabilities (SAPs) computed in this chapter, we show that the probabilistic approaches have only limited performance advantages over deterministic ones. We first consider a static network scenario as originally considered in the seminal paper by Eschenauer and Gligor [9], where any node capture happens after the establishment of all pairwise links. In this scenario, we show that the deterministic approach can achieve a performance as good as the probabilistic one. In a mobile network scenario, however, the probabilistic key management as described in [9] can lead to a SAP of one order of magnitude larger than the one in a static network due to node fabrication attacks.

The above analysis motivates us to propose two low-cost secure-architecture-based techniques to improve the security against such attacks. Our new architectures, specifically targeted at the sensor-node platform, protect long-term keys using a root of trust embedded in the hardware System-on-a-Chip (SoC). This prevents an adversary from extracting these protected long-term keys from a captured node to fabricate new nodes. The extensive simulation results show that the proposed architecture can significantly decrease the SAP and increase the security level of key management for mobile ad hoc networks.

Finally, we develop an analytical framework for the on-demand key establishment approach. We propose a novel security metric, the REM resilience vector, to quantify the resilience of any key establishment schemes against Revealing, Erasure, and Modification (REM) attacks. Our analysis shows that previous key establishment schemes are vulnerable under REM attacks. Relying on the new security metric, we prove a universal bound on achievable REM resilience vectors for any on-demand key establishment scheme. This bound that characterizes the optimal security performance analytically is shown to be tight, as we propose a REM-resilient key establishment scheme which achieves any vector within this bound. In addition, we develop a class of low-complexity key establishment schemes which achieve nearly optimal REM attack resilience.