# Trust and Mobility-Based Protocol for Secure Routing in Internet of Things
###### Abstract  
In the Internet of Things (IoT), the de facto Routing Protocol for Low Power and Lossy Networks (RPL) is susceptible to several disruptive attacks based on its functionalities and features. Among various RPL security solutions, a trust-based security is easy to adapt for resource-constrained IoT environments. In the existing trust-based security for RPL routing attacks, nodes' mobility is not considered or limited to only the sender nodes. Similarly, these trust-based protocols are not evaluated for mobile IoT environments, particularly regarding RPL attacks. Hence, a trust and mobility-based secure routing protocol is proposed, termed as SMTrust, by critically analysing the trust metrics involving the mobility-based metrics in IoT. SMTrust intends to provide security against RPL Rank and Blackhole attacks. The proposed protocol is evaluated in three different scenarios, including static and mobile nodes in an IoT network. SMTrust is compared with the default RPL objective function, Minimum Rank with Hysteresis Objective Function (MRHOF), SecTrust, DCTM, and MRTS. The evaluation results indicate that the proposed protocol outperforms with respect to packet loss rate, throughput, and topology stability. Moreover, SMTrust is validated using routing protocol requirements analysis to ensure that it fulfils the consistency, optimality, and loop-freeness. interact of things; IoT security; routing; RPL; RPL attacks; Rank; Blackhole; trust +
Footnote †: journal:  
* [2022] 22220  
a considerable number of routing attacks [13] involving RPL-specific attacks, based on RPL features, and WSN-inherited attacks, that is, attacks derived from wireless sensor networks (WSNs) [14] because both IoT and WSNs domains are related to each other [15]. In IoT networks, it is challenging to detect and defend routing attacks because of devices' nature and IoT systems' unique requirements [16]. Figure 1 illustrates an overview of IoT applications, layers, network models, components, security, privacy, and trust, including the RPL attacks and existing security techniques. This research work intends to focus specifically on the security of the RPL routing protocol. The routing attacks considered in this research include the Rank attack and the Blackhole attack in RPL. These two attacks have a high impact on routing process, among others. Fake rank information is advertised by a malicious node in a Rank attack. As a result, the routing information is forwarded to the sink node through malicious nodes by selecting it as a preferred parent. Similarly, the occurrence of Blackhole attack in routing causes dropping of packets and data loss. The widespread adoption of RPL protocol in smart healthcare, smart homes, smart cities, and the smart world [17] appeals that it is imperative to investigate these security attacks [18]. In the existing literature, numerous methods for solving the security of IoT routing are suggested, such as machine learning [19], intrusion detection systems (IDS) [20], trust [21; 22], and other mitigation approaches [23; 24]. The conventional security practices are inadequate to address the specific security needs of IoT. Because of its simple deployment and incorporation into the IoT network, the trust-based approach is a feasible alternative to provide RPL security. Furthermore, node mobility is not considered in current trust-based methods [25; 26] or is inadequate for mobile sink nodes [27], especially for defence against Blackhole and Rank attacks in RPL. Hence, the proposed model scrutinizes the mobility metrics for trust computation. In addition, the proposed solution is investigated and evaluated for a dynamic IoT environment, considering mobile sender nodes along with mobile sink nodes. Figure 1: An Overview of IoT Applications, Layers, Network Models, Components, Security, and RPL Attacks. This research aims to develop a trust-based routing protocol for IoT applications and improve security in RPL at the IoT network layer against Rank and Blackhole attacks.