# Defense and Security Mechanisms in the Internet of Things: A Review
## 1 Introduction  
Smart devices have become a part of our daily life. Some examples include intelligent light bulbs, motion sensors, cameras, and vacuum cleaners in smart home devices. This is because, through them, we can manage and control the various aspects of our homes in real time from a remote location. Smart devices can also improve efficiency and quality of life in smart cities (for example, intelligent street lighting, traffic, or waste management systems). In industry, intelligent devices help monitor and optimise production processes and automate production lines. Health care (such as heart rhythm control), agriculture (such as soil moisture monitoring), the transport sector, sports, and security can also utilise these devices. Smart devices can function independently or receive remote control and monitoring. These devices can also perform specific actions without human intervention [1, 2, 3, 4]. The Internet of Things (IoT) denotes a worldwide network of interconnecting devices capable of collecting data from the environment, analysing the aggregated information, and reacting accordingly based on autonomous or human-directed commands. Throughvast arrays of sensors and actuators amalgamated into one coordinated system, IoT technologies will continue to drive innovation in how we interact with appliances, vehicles, infrastructure, and more. IoT integrates the physical world with the Internet, creating more effective, intelligent, and innovative solutions. This connection to the network enables everyday objects, industrial machines, and the entire urban infrastructure to become more intelligent and unlock additional possibilities. IoT creates a coherent system that enhances the capabilities of participating entities and introduces network intelligence to facilitate decision-making and easy data exchange [5; 6]. The use of smart devices has its advantages and disadvantages. First, these devices can be designed to perceive their working environment, gather information, and carry out particular tasks depending on particular circumstances [7; 8]. For instance, in the context of intelligent vehicles, we can enhance the protection of road users (pedestrians, cyclists, drivers) through the monitoring of their well-being as well as the vehicle itself [9; 10]. Conversely, using smart devices may engender issues related to technology or security. Establishing networks that connect such devices frequently necessitates the development of an infrastructure that integrates several technologies. Issues emerge with device interoperability, restricted processing and storage capacities, or Internet connectivity [7]. These challenges may pertain to communication security, users, and data. Communication between IoT devices can be facilitated by employing a wireless network that serves users operating within a specific building, utilising a local wireless network with Internet connectivity, or establishing Internet connections that enable each device to access the Internet. Network administrators must guarantee communication security between devices and users and the integrity of sent and processed data in each specified solution [11]. Threats to internet access include hacking of users, devices, data, and complete computer systems and networks. Many protective countermeasures are also possible in IoT to prevent cyber-attacks [12; 13]. We can categorise several forms of attacks. For example, in a sensor node/IoT device-based capture attack, the attacker gains control over the device to control the network. He then separately withdraws the node from the network and replaces it as a malicious node [14; 15; 16]. In an impersonation attack, the attacker abuses the identities of different network entities, including a user, a server, and an IoT device [17; 18]. In a guessing assault, the assailant attempts to deduce the user's password or other authentication credentials [19]. In a significant compromise impersonation attack [20], the adversary leverages the client's certificate on its device to become the client.