Wireless sensor networks are deployed in unattended and hostile environment for many applications such as battlefield surveillance. The WSN applications may require knowing the locations of the node in the network to assist in neighbour discovery, selective information sharing and so on. The trivial approach to node localization is to equip each node with GPS. However, the cost and size of GPS enabled nodes make it impractical for resource-constrained, low cost WSNs. GPS-free node localization has been addressed using two different approaches - Beacon Based (BB) and Without Beacon Based (WBB). In BB approach, few nodes aware of their locations serve as beacons to help other nodes in the network localize themselves. In WBB approach, nodes need to localize themselves with the help of their neighbours only. Although, knowledge of nodes' location within network is desirable, exposure of node location information to adversary may lead to undesirable consequences, such as ease of planning for node capture attack, and hence the need of secure localization. The BB approach has been studied extensively under adversarial model and many algorithms based on BB approach have been proposed in literature in order to localize nodes in a secure manner. In contrast, WBB approach for node localization under adversarial model has not received substantial attention from researchers. In this chapter, we discuss static and dynamic key settings for node localization using WBB for node localization under adversarial model. We consider the Localized Combinatorial Keying (LEAP) and Localized Encryption and Authentication Protocol (LEAP) as the building block and propose a protocol for pair-wise key establishment and key revocation to facilitate secure node localization without using beacon nodes in mobile sensor networks, aiming at providing resilience against node impersonation attack and thus minimizing the impact of node capture threats. We provide a comparison of the improved protocol with other related protocols. We show that the improved protocol provides effective node localization in a secure manner with minimal node capture threats.
TopIntroduction
WSN is a network of sensor nodes that communicate via wireless links to cooperatively monitor the environment or object. Sensor nodes in a WSN are typically deployed in unattended, hostile terrains and therefore, are mostly not aware of their locations. Many WSN applications require the nodes to know their locations after the network deployment. For this purpose, sensor node localization process is used. The advantages of knowing the location information of sensor nodes in WSN include:
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Network coverage checking and location-based information querying.
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Selective forwarding instead of broadcasting information.
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Neighbour discovery.
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Data aggregation after finding neighboring node.
In the localization process, sensor nodes in a WSN determine spatial relationships between themselves (Srinivasan & Wu, 2007; Rasmussen, Capkun, & Cagalj, 2007; Mi, Stankovic, & Stoleru, 2012). The determination of spatial relationship signifies that the nodes are able to assign location coordinates to each other either with reference to a coordinate system localized to a particular network or with reference to a global coordinate system such as GPS (Global Positioning System). Broadly, the approaches used toward localization consist of two types of nodes:
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Beacon Node / Anchor Node: Node, who knows its physical location (either via GPS receiver or by manual configuration).
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Regular Node / Non-Beacon Node: Node, who does not know its position and no special hardware is required to acquire its location information.
Beacon-Based Approach
Beacon-based (BB) approach uses Beacon node(s) as the basis for computing the location coordinates of other non-Beacon nodes. The idea is to implement the Beacon node with directional antennas and the non-Beacon nodes localizing themselves based on the range of whichever antenna they belong to. Naturally, the security is an important concern in BB approach when an adversary attempts to compromise some Beacon nodes (Liu, Ning, Liu, Wang, & Du, 2008).
However, In the context of node localization in WSN that is inherently distributed in nature, BB approach does not seem to be suitable because (i) in BB approach, a large number of beacon nodes are required to localize all non-beacon nodes; (ii) BB approach is not scalable well in comparison to WBB approach; (iii) in BB approach, localization is completely dependent on Beacon nodes.
Without Beacon-Based Approach
When the network does not have beacon/anchor nodes, the regular nodes may coordinate with their neighbour nodes and build a localized coordinate system wherein a node's location is determined in reference to its neighbour nodes. However, when communication is established with other networks, the local coordinate system can be converted to a global coordinate system with the help of the central authority such as base station. One of the main advantages of WBB approach is scalability. Generally, the WBB approach involves following three steps to establish a localized coordinate system in the network.
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Discovery of one-hop neighbors and sharing a secret pair wise key with them.
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Calculation of distance to each neighboring node.
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Assigning coordinates to neighboring nodes based on the distance measurements.
The main aspect in WBB approach of node localization is the discovery of neighbours and establishing secret pair-wise key with them. Once the communication between a pair of nodes is secured via a pair-wise key, integrity of distance measurement and coordinate assignment is ensured and hence the correctness of the localization process.