# An Efficient Location Verification Scheme for Static Wireless Sensor Networks
## 1 Introduction  
Wireless sensor networks (WSNs) have been one of the most popular topics for many years. The networks consist of a large number of low-cost sensors with wireless communication interfaces and enable many applications, such as environment monitoring, target tracking or rescuing. In those applications, location information plays an important role to make the sensed data more meaningful. Furthermore, the delivery of the data relies on the position of sensors when geographical routing is used as the underlying routing protocol. To enable those applications, sensors usually get their positions by the location estimation process called localization. One of the famous localization methods is Global Positioning Systems (GPS), but other schemes, such as magnetic positioning, dead reckoning and data-fusion-based positioning, are also possible. For instance, anchor sensors who are equipped with video and a compass can be used to estimate the location when GPS is not available [1]. Since many of the localization processes are designed in a benign environment where no attackers exist, it may not be possible to provide the correct location with any attacker. Thus, the location estimation process known as secure localization has been proposed to protect the localization by utilizing hop-distance information, game-theory or trust models [2; 3; 4; 5; 6; 7; 8; 9]. Unfortunately, they are not enough to eliminatethe wrong location estimations in some situations, e.g., reference sensors that provide the absolute coordinate are compromised or sensors report a false location by themselves. Hence, the location verification process that checks the reported location of sensors becomes necessary. Figure 1 shows the general concept of the localization and location verification. As shown in Figure 1a, localization generally measures the distances or angles of radio arrival between a set of reference sensors who know their location and the target sensor who wants to know its location. Based on the measurements, the location of the target sensor is determined. Secure localization uses some physical constraints, such as distance inconsistency between sensors, to prevent any malicious sensors from cheating in the location estimation process. In the case of location verification, it usually occurs when the acquired location is used in an application. For example, if the location of a sensor is suspicious, a sensor that is called the verifier collects the necessary information and performs location verification as shown in Figure 1b. This location verification problem can be formulated in many different mathematical ways by reflecting the characteristics of the algorithms [10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21]. Location verification schemes in WSNs can be categorized as on-spot and in-region verification [15]. On-spot verification is to verify whether the true location of a sensor is the same as its claimed location, and in-region verification is to verify whether a sensor is within a certain region. In each category, several location verification schemes have been proposed to check the reported location of sensors with special requirements [10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21]. The special requirements, such as special hardware, the active participation of neighbors, a dedicated verifier and a trusted third party, impose a burden on the sensors in terms of hardware cost, communication overhead and computation overhead. In this paper, we propose an efficient location verification scheme in static WSNs, which falls into the on-spot verification. To eliminate any special requirements that cause communication and computation overhead, the proposed scheme utilizes the common knowledge between claimant and verifier: one claiming its claimed location and the other trying to verify the location, respectively. The common knowledge is called the MSR (mutually-shared region) token and should be some information that can be derived exclusively between claimant and verifier.