A Probabilistic Approach to Location Verification in Wireless Sensor Networks Eylem Ekici Department of Electrical and Computer Engineering Ohio State University, Columbus, OH 43210 Email: ekici@ece.osu.edu Janise McNair and Dawood Al-Abri Department of Electrical and Computer Engineering University of Florida, Gainesville, FL 32611 Email: mcnair@ece.ufl.edu, alabri@ufl.edu Abstract— Security plays an important role in the ability to deploy and retrieve trustworthy data from a wireless sensor network. Location verification is an effective first line of defense against attacks which take advantage of a lack, or compromise, of location information. In this work, a probabilistic approach to location verification in dense sensor networks is proposed. The proposed Probabilistic Location Verification (PLV) algorithm leverages the probabilistic dependence of the number of hops a broadcast packet traverses to reach a destination and the Euclidean distance between source and destination. A small number of verifier nodes determine the plausibility of the claimed location, which is represented by a real number between zero and one. Using the calculated plausibility metric, it is possible to create arbitrary number of trust levels in the location claimed. Simulation studies verify that the proposed solution provides high performance in face of various types of attacks. Keywords Wireless Sensor Networks, Localization, Location Verification I. I NTRODUCTION Wireless sensor networks (WSNs) typically consist of a large number of simple and inexpensive sensor devices equipped with wireless communication interfaces. An impor- tant concern for numerous applications of WSNs is the ability to validate the integrity of the network and the retrieved data. Various types of security attacks include: (1) the injection of false information into the regular data stream, (2) the alteration of routing paths due to malicious nodes advertising false positions (sink holes and worm holes), and (3) the forging of multiple identities by the same malicious node (Sybil nodes). Thus, location-based security plays an important role in the trustworthiness of WSNs and obtained results. Although secure, point-to-point communication mecha- nisms can potentially prevent introduction of new adversary nodes into communication stream, it is likely that a compro- mised node infiltrates such mechanisms. Location Verification emerges as a lightweight first line of defense, which ensures that the information and its claimed source location are as- sociated with a high level of trust. Information for which the source location cannot be verified is deemed not trustworthy and rejected to ensure the integrity of accepted data. Over the past five years, researchers have developed many protocols for localization [1], [2], [3]. However, researchers have just recently begun to address the issue of security in localization [4], [5], [6]. In [4], a technique is proposed that combines conventional multilateration with distance bounding for computation and verification of sensor positions. However, sensors must have a bounded processing time which may not be met by most existing hardware. In [5], a secure positioning technique using directional antennae is proposed. Several techniques have been proposed using statistical methods [6], consistency among beacon signals, and voting schemes [7] to achieve robustness. Recent research also demonstrates that location verification can be combined with a non-secure local- ization scheme to produce a system that is more robust and resilient to attack than localization alone. In [8], a protocol is described that verifies the presence of a node using radio frequency and sound. In [9], a hybrid system is proposed that combines secure location computation with a location verification step that ensures a node cannot claim to be closer to a locator (reference node) than its actual distance. However, this approach requires a secure localization scheme. In this work, a probabilistic approach to location verification in dense and random WSNs, Probabilistic Location Verifica- tion (PLV) algorithm, is proposed. PLV leverages the proba- bilistic dependence of the number of hops a broadcast packet traverses to reach a destination and the Euclidean distance between the source and the destination. A small number of verifier nodes calculate the likelihood that a broadcast packet that contains the geographic location of a node is received over a number of hops recorded in the packet. Observations of individual verifiers are combined to determine the plausibility of the location claim, a number between zero and one. It is the level of confidence that the claimed location results in the observed number of hops from the claimant source to all verifiers. The plausibility can be compared against a threshold to validate the claimed location. The non-binary property of plausibility also enables the use of multiple levels of trust in the claimed location. The salient properties of our proposed PLV algorithm can be summarized as follows: 1) Sensor nodes do not need to be equipped with special- ized hardware. 2) Only a small number of specialized verifiers are needed. 3) The plausibility of a location claim is expressed as a real-number, not a hard binary decision. 4) The PLV algorithm is resilient against a number of at- tacks and provides graceful degradation in performance. This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the IEEE ICC 2006 proceedings. 1-4244-0355-3/06/$20.00 (c) 2006 IEEE