Abstract-Node identification is one of the most important issues to wireless sensor network security. Current approaches use cryptographic authentication and certification tools to ensure the node identification, while this paper introduces an intuitive method to identify a node by measuring its clock skew. This method is based on our observation that every sensor node has a unique clock skew value that is different from any other node. We adopt Flooding Time Synchronization Protocol (FTSP) as the measuring tools, and the experimental data show that almost all measured clock skews of one sensor node vary inside a tiny bound. For any two nodes that their clock skews are very close to each other, a classifying function is proposed to check the line continuity of contiguous measured clock skews. The proposed method has successfully identified every node in our experiments, and its applications like Sybil attack detection is also discussed.

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Along with the growth of cloud computing and mobile devices, the importance of client device identity concern over cloud environment is emerging. To provide a lightweight yet reliable method for device identification, an application layer approach based on clock skew fingerprint is proposed. The developed experimental platform adapts AJAX technology to collect the timestamps of client devices in the cloud server during connection time, then calculate the clock skews of client devices. Few methods based on linear regression and piecewise minimum algorithm are developed to optimize the precision and shorten timestamp collection process. A jump point detection scheme is also proposed to resolve the offset drifting problem, which is usually caused by switching network or temporary disconnection. Finally, two experiments are conducted to study the effectiveness of clock skew fingerprint, and the results illustrate that the false positive rate and the false negative rate, in the worst case, are both no more than 8% when the tolerance threshold is set appropriately.

SUMMARYThis work aims to address the security vulnerability of the Flooding Time Synchronization Protocol (FTSP), which is currently one of the most popular approaches for time synchronization in wireless sensor networks. FTSP has advanced features, such as implicitly dynamic topology and high time accuracy, but still has unresolved security issues. In order to defend against attacks from malicious nodes, we propose several technologies to reinforce the structure of FTSP. First, a reference node selecting mechanism is proposed to reduce the effect of multiple reference nodes, and four filters are proposed to defend against seqNum attack, global time attack and node replication attack. Experiment results show that the proposed sequence number blacklist filter and the global time blacklist filter are effective in defending against the aforementioned attacks. Second, a new root selection mechanism is proposed to secure the process of updating the root node. Combining the root selection mechanism with the global time black list filter, the proposed mechanisms successfully defend against traitor attacks on FTSP in our experiment. Copyright © 2013 John Wiley & Sons, Ltd.

A fundamental building block in distributed wireless sensor networks is time synchronization. Given resource constrained nature of sensor networks, previous research has focused on developing various energy efficient time synchronization protocols tailored for these networks. However, many of these protocols have not been designed with security in mind. In this paper, we describe FTSP which is one of the major time synchronization protocols for sensor networks. We outline the adverse effects of the time synchronization attacks on some important sensor network applications, and explain the set of possible attacks on FTSP. We then propose a number of countermeasures to mitigate the effect of the security attacks. We implement these attack scenarios on a sensor network testbed and show the extent each attack is successful in desynchronizing the network. Finally, we implement the countermeasures on our sensor network testbed to validate their usefulness in mitigating security attacks. We show that adding a sequence number filter to the original FTSP helps mitigate the effect of attacks on this protocol.

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