# Secure Localization in the Presence of Colluders in WSNs
## 2 Related Work  
The impact of the wormhole attack on the DV-Hop localization algorithm is analysed in [4]. Based on the analysis results, a label-based DV-Hop secure localization scheme is proposed to defend against the wormhole attack. The proposed scheme assumes an ideal and homogeneous communication range for all the sensors. The simulation results prove the effectiveness of the proposed scheme. A secure and scalable geographic opportunistic routing (SGOR) protocol [7] is proposed to defend against a wide range of attacks. SGOR employs a distributed location verification algorithm to address the location-spoofing attack. In order to detect this attack, the sensor nodes exchange messages between them and records the received signal strength (RSS) measurements. In the routing layer, an indirect trust model is proposed to response to different attacks based on the location verification algorithm. Simulation results prove that SGOR has an excellent performance with acceptable overhead under various attacks. Another secure region-based geographic routing (SRBGR) protocol is proposed in [23]. The basic idea behind SRBGR is to increase the number of legitimate nodes participating in communication process when the number of attackers increases by applying different message contention priorities. SRBGR uses a bound dynamic window to provide sufficient collection time for packets. It also uses the verification cost to validate node's location in order to identify and isolate the attacker during priority selection criteria. Simulation results demonstrate that SRBGR increases the network performance in terms of the packet delivery ratio and isolates attacks such as Sybil and blackhole attacks. A secure and reliable prediction-based target tracking (SRPTT) protocol [6] is proposed to consider both security and object tracking tasks simultaneously. The basic idea behind SRPTT is to ensure security using reputation based trust concept for individual sensor nodes. The possible attack scenarios for SRPTT are analysed and simulation results show that the proposed protocol allows the network to retain the reliability of tracking data even in the presence of compromised nodes, thereby achieving secure and reliable object tracking process. The work in [24] analyses existing techniques for collusion prevention. Results show their inadequacy for prevention of colluders in WSN scenarios. The work in [25] addresses bounded errors conditions to guarantee the security of the process conducted by sensor nodes using a two-dimensional distance-based estimation process, executed in the presence of cheating beacon nodes. Three algorithms driven by distance-based techniques are developed to guarantee bounded error localization under cheating beacons. Cheating beacons are defined as beacons providing a false distance between nodes. The goal of the attackers generating the cheating beacons is to lead location-unknown nodes to miscalculate their position. Accuracy and efficiency of the algorithms are measured via numeric simulation. A positioning process called tolerant majority colluding attacks (TMCA) [18] assumes the cooperation of non-beacon WSN neighbour nodes in order to address adversarial scenarios such as wormholes, replay and Sybil attacks. TMCA is validated under situations where the number of malicious nodes is larger than the number of benign nodes. TMCA allows location-unknown nodes to compute their position using distance bounding techniques. The underlying technique relies on the use of _maximum likelihood estimation_, in order to correlate the coordinates and the distance measurements received from a reference beacon. Authors in [24] observed a lack of evidence with regard to collaboration (e.g., amount of exchanges) or collusion of adversarial nodes in TMCA. The authors in [24] also illustrate attack possibilities in some other protocols similar to TMCA reported in [26]. The following observations are made.