Toward secure and scalable time synchronization in ad hoc networks

Time synchronization is crucial in ad hoc networks. Due to the infrastructure-less and dynamic nature, time synchronization in such environments is vulnerable to various attacks. Moreover, time synchronization protocols such as IEEE 802.11 TSF (Timing Synchronization Function) often suffer from scalability problem. In this paper, we address the security and the scalability problems of time synchronization protocols in ad hoc networks. We propose a novel suite of time synchronization mechanisms for ad hoc networks based on symmetric cryptography. For single-hop ad hoc networks, we propose SSTSP, a scalable and secure time synchronization procedure based on one-way Hash chain, a lightweight mechanism to ensure the authenticity and the integrity of synchronization beacons. The ‘‘clock drift check’’ is proposed to counter replay/delay attacks. We then extend our efforts to the multi-hop case. We propose MSTSP, a secure and scalable time synchronization mechanism based on SSTSP for multi-hop ad hoc networks. In MSTSP, the multi-hop network is automatically divided into single-hop clusters. The secure intra-cluster synchronization is achieved by SSTSP and the secure inter-cluster synchronization is achieved by exchanging synchronization beacons among cluster reference nodes via bridge nodes. The proposed synchronization mechanisms are fully distributed without a global synchronization leader. We further perform analytical studies and simulations on the proposed approaches. The results show that SSTSP can synchronize single-hop networks with the maximum synchronization error under 20 ls and MSTSP 55–85 ls for multi-hop networks, which are, to the best of our knowledge, among the best results of currently proposed solutions for single-hop and multi-hop ad hoc networks. Meanwhile, our approaches can maintain the network synchronized even in hostile environments. 2007 Elsevier B.V. All rights reserved.