# A Trust-Based Model for Secure Routing against RPL Attacks in Internet of Things
###### Abstract  
In IoT networks, the de facto Routing Protocol for Low Power and Lossy Networks (RPL) is vulnerable to various attacks. Routing attacks in RPL-based IoT are becoming critical with the increase in the number of IoT applications and devices globally. To address routing attacks in RPL-based IoT, several security solutions have been proposed in literature, such as machine learning techniques, intrusion detection systems, and trust-based approaches. Studies show that trust-based security for IoT is feasible due to its simple integration and resource-constrained nature of smart devices. Existing trust-based solutions have insufficient consideration of nodes' mobility and are not evaluated for dynamic scenarios to satisfy the requirements of smart applications. This research work addresses the Rank and Blackhole attacks in RPL considering the static as well as mobile nodes in IoT. The proposed Security, Mobility, and Trust-based model (SMTrust) relies on carefully chosen trust factors and metrics, including mobility-based metrics. The evaluation of the proposed model through simulation experiments shows that SMTrust performs better than the existing trust-based methods for securing RPL. The improvisation in terms of topology stability is 46%, reduction in packet loss rate is 45%, and 35% increase in throughput, with only 2.3% increase in average power consumption. a _et al._ Article  
20222202222202  
and requirements of IoT systems and devices. Provided the prevalent applications of RPL for a smart world [10], it is imperious to deal with related security attacks [11; 12]. Figure 1 presents the overview of RPL network, functional flow, and illusion of intrusion by an attacker in an RPL Destination Oriented Directed Acyclic Graph (DODAG). Some of the attacks in RPL include, Rank attack, Blackhole attack, Version number attack, Sinkhole attack, Wormhole attack, and DODAG Inconsistency attack. In the existing literature, various methods for solving the IoT routing security are proposed, including intrusion detection systems, machine learning, and trust-based techniques [13]. Because of its simple deployment and incorporation into the IoT network, the trust-based approach is a potential way to fulfil RPL security needs. Several trust-based solutions have been proposed by researchers, specifically for the security of RPL-based IoT. In existing trust-based security solutions, node mobility is not at all considered [14; 15] or is inadequate for mobile sink nodes [16], in RPL-based IoT for defense against routing attacks. The Rank and Blackhole attacks in RPL are the most disruptive routing attacks, among others. In a Rank attack, false rank information is advertised by the malicious node. As a result, the malicious node is selected as a potential parent. Similarly, the occurrence of Blackhole attacks in routing causes the dropping of packets and data loss. Trust is a term defined for affiliation between two entities, where one entity is the evaluator, known as trustor, while the other is being evaluated, known as trustee [17]. In a trust relationship, the trustor must have confidence in the trustee regarding belief, benevolence, and honesty. Therefore, the trust value must make sure that the trustee would not betray the trustor by performing any malign actions [18]. The notion of trust is being used in various disciplines, including sociology as well as computer science, particularly, communications, networks, and the IoT [19]. The behaviour, integrity, and reliability of a sensor node are termed as trust in sensor networks in the domain of computer science. In the network and communications security, trust is a relation between participating entities. Trust relationship relies on past experiences and current circumstances of entities in the network and determines the efficiency, reconfigurability, and scalability. Certain metrics are used for a node's cumulative trust value estimation, which reflects its legitimacy in the network.