Devices like the Internet of Things (IoT) have a significant presence in our daily lives owing to the technological revolution, wireless devices, and communication systems. IoT has become a vital part of the digital era of Industry 4.0. The ability to bring physical things into the digital world is becoming more likely because of technology. Applications of IoT can be utilized in various ways to assist systems and businesses in simplifying, improving, automating, and controlling processes. IoT can also be used for delivering important data, activity performance, or even environmental factors that have to be monitored continuously and remotely. IoT applications can therefore help with the creation of new systems and business strategies, as well as provide businesses with the instant data they need to create products and services.
1. Smart City
A smart city is a technologically advanced metropolitan region that collects information using different electronic techniques, voice recognition technologies, and sensors. The data is utilized to successfully handle assets, services, and programs; in turn, the information is being used to function smoothly throughout the city. Data obtained from community members, equipment, structures, and assets are processed and analyzed to track and maintain road and transport infrastructures, energy plants, utilities, water system connectivity, waste management, preventing crime, data management, education institutions, libraries, healthcare facilities, and other community programs. A smart city is a collection of different sensors and equipment to monitor, report, and process to manage the resources of the infrastructure effectively. Using the information gathered from the wireless sensors, the system will learn and make decisions to provide beneficial outcomes to the people. Compared to the healthcare, water supplies, and environment surveillance in the current urban areas, a smart city will be able to connect the citizens and the required services in a better way 
. It is necessary to protect both the residents’ privacy and the information system’s integrity. Sensitive information is being gathered by sensing devices, which makes it vulnerable to cyberattacks.
2. Internet of Medical Things (IoMT)
The integration of health features into IoT devices makes the environment an IoMT. With the advancement of technology, the usage of IoMT devices is increasing. Moreover, the COVID-19 situation limits face-to-face meeting between patients and doctors. The pandemic has created a new era of IoMT for providing treatment to patients 
. IoMT is making a network of people and medical devices (wireless medical devices and implanted medical devices). It utilizes wireless communication (Bluetooth, WiFi, 3G, 4G, 5G, ZigBee, etc.) to exchange health data with medical facilities like doctors, hospitals, medical experts, etc., 
. With the advancement of microelectronics, medical devices have become intelligent and can monitor and report physical conditions such as blood pressure, heartbeat, oxygen level, etc. The devices can be placed in the body in the form of watches, belts, shoes, clothes, necklaces, etc., 
. Moreover, IoMT has become the most significant change among the development in the medical sector as it brings not only the aged people but also every aged sick people in continuous monitoring and treatment. Especially people suffer even after recovering from COVID-19, and IoMT provides immediate treatment if necessary. Many healthcare systems from all over the world adopt the IoMT system to provide treatment. However, nearly 50% of IoMT equipment is susceptible to attack, as per the 2020 CyberMDX research. IoMT network is distinct from other systems in that they have the potential to impact patients’ lives and raise privacy problems if their identities are divulged 
. Maintaining security and privacy is the primary concern of the IoMT system. According to a research from cybersecurity firm Critical Insights, cybersecurity incidents reached an all-time peak in 2021, compromising a record quantity of patients’ personal health data. Healthcare attacks harmed 45 million people in 2021, rising from 34 million in 2020. As per the research, the number of breached data has tripled within only three years, up from 14 million in 2018 
3. Smart Grid
A smart grid is an electrical system that contains several efficient and energy efficiency features such as infrastructure for intelligent metering, intelligent power panels, smart equipment, control system, alternative/renewable energy, etc. The term “smart grid” refers to a concept that encapsulates the entire power generation and distribution system in a single frame. It is an electricity system built on digital technology that uses two-way digital communication to supply electricity to consumers. To put it another way, a Smart Grid is a grid that makes the entire system smarter or cleaner. Clean energy is presently in high demand all around the world. In 2003, the first time the term “Smart Grid” was stated by Michael T. Burr in an article 
. Smart grid technology allows real-time monitoring, coordination, and control of the electric energy grid via communication networks between physical components, resulting in more effective and economical grid management. The widespread availability of Internet connectivity in most houses has made the smart grid more viable to adopt. The smart grid consists of Supervisory Control And Data Acquisition (SCADA), Energy Management System, Grid Communication Systems, and Distributed Energy Resources (DERs). In a smart grid system, users’ data privacy and security are crucial and challenging issues. A cyber-physical exploit is a safety failure in cyberspace that negatively affects a CPS’s physical environment 
. There have been a number of significant cyber-physical incidents have been reported in the sector in recent years. A computer worm called “Stuxnet” leveraged four zero-day flaws and cryptographically signed certificates to evade intrusion detection. It hit the Iranian nuclear fuel enrichment complex in June 2010 where the programmable logic controllers (PLC) of the SCADA system were the targets 
. Three Ukrainian electric power distribution firms were hacked in a coordinated operation in December 2015. Thirty substations were blacked out for almost three hours, resulting in 225,000 consumers experiencing wide-area power outages. To frustrate claims of disruptions, a telephonic DoS attempt was conducted while authorized members’ virtual private network accounts were stolen using the Black-Energy3 virus 
. At present different AI based techniques are used to detect and defend the mechanism of the smart grid security system.
4. Internet of Vehicles (IoV)
With the development of industry, the number of vehicles is increasing rapidly. The increment of vehicles raises security concerns that trigger secure communication. IoV will lead industry 4.0. It is certain that the IoV will be bright and profitable in the future, offering improved road safety, reduced environmental effects, better space utilization, and cost control. The IoV, often known as smart transportation or connected cars, is a framework comprising vehicles, smartphones and wearables, roadside equipment, and a network. People, cars, and numerous IoT devices that are part of the transport system communicate over IoV 
. Transportation, production, energy, software, and other industries are all affected. The IoV ecosystem includes hardware, software, services, and multiple network technologies ranging from Bluetooth and cellular to Wi-Fi and 5G, as well as several types of communication (V2V, V2X, and so on). Vehicle-to-vehicle and vehicle-to-infrastructure communication systems are combined to create the vehicular ad hoc network or VANET, and the term IoV has developed from the notation VANET. The combination of functionalities such as sensing units, control platforms, and various computer resources makes each vehicle in IoV an intelligent object. Each vehicle connects to any entity via a V2X communication architecture. The aim of IoV, also known as V2X, is safe driving by reducing accidents, alleviating traffic congestion, providing low traffic route information, and providing other information services. Every vehicle in the IoV network interacts with all other things that could have an influence on it. V2X mainly includes vehicle-to-vehicle (V2V), vehicle-to-sensors (V2S), vehicle-to-infrastructure (V2I), vehicle-to-network (V2N), and vehicle-to-pedestrian (V2P) communication. Nevertheless, roads can be seized by modifying or changing data or making wrong decisions due to the receipt of prank data 
. To avoid these kinds of situations, it is required to develop a robust authentication framework that can resist security vulnerabilities and can conduct verification within milliseconds.