## 2 Literature Review on IoT and Lightweight Security Protocols
### Challenges and Requirements in Implementing IoT  
Table 4 presents a summary of several research papers that overview the challenges and the requirements in implementing IoT. Next, the notable points of each one of these papers are summarized. [PERSON] et al. [29] presented an overview of the challenges and requirements in building a secure IoT system. They gave a taxonomy and compared different security protocols proposed for wireless sensor networks and IoT with respect to how they employ key bootstrapping mechanisms. They provided a review of ongoing research initiatives in the field of security for IoT, which they categorized into two types: solutions that rely on asymmetric key schemes (or public-key encryption) and key management solutions that pre-distribute symmetric keys. [PERSON] and [PERSON] [30] reviewed the development of IoT security research from 2016 to 2018. In particular, they discussed the challenges in applying security mechanisms in IoT and its attack vectors. Another study by [PERSON] et al. [9] identified the latest security risks for IoT systems. It first described some communication protocols at various layers of the protocol stack, from Bluetooth Low Energy (BLE) at the physical/data link layer to MQTT at the application layer, and their security features and vulnerabilities. The security attacks described in the paper are classified in terms of protocol-based attacks, such as pre-shared key attacks and sniffing attacks, or data-based attacks, such as hash collision (to attack the integrity of the data) and denial of service (to attack the availability of the data or service), but no particular application is referenced. They also compared other research works in terms of confidentiality, integrity, and availability, but these works and techniques are presented only at a high level. In particular, one new method uses ECC and fully homomorphic encryption (FHE) to improve integrity, and another one uses MQTT and a Robot Operating System (ROS) to improve authentication for robotic systems in industrial settings. As future trends, the authors presented Artificial Intelligence (AI), blockchain, and Elliptic Curve Cryptography (ECC) as key technologies that should be integrated into IoT security schemes. [PERSON] et al. [31] discussed the current status and how to design IoT security. They reviewed the IoT security panorama, by providing a taxonomic analysis from the perspective of the three layers of the IoT system model: (1) perception; (2) transportation; and (3) application layers. [PERSON] et al. [32] investigated IoT security from data perspectives by combining the concept of IoT architectures with data life cycles. They proposed a three-dimensional approach to exploring IoT security with the one-stop, multi-stop, and end application dimensions. They also analyzed the latest developments in IoT security. [PERSON] and [PERSON] [33] studied IoT applications in different fields and IoT architecture layers, including basic functionalities, devices, protocols, and security threats at each layer. They also discussed topics on IoT security requirements and cyberattacks. [PERSON] et al. [34] investigated security and privacy issues in IoT systems at each layer in the IoT protocol stack, and they identified the underlying challenges and security requirements. A brief overview was given on existing security solutions to safeguard IoT systems at each layer. [PERSON] et al. [35] reviewed cloud-based IoT security solutions and communication between IoT devices and applications from 2013 to 2019. They discussed open issues for securing cloud-based IoT systems. Then, they analyzed security requirements in terms of access control, integrity, and authentication. [PERSON] et al. [36] discussed security challenges for Industrial IoT of Internet 4.0. One important difference when using IoT in industrial settings is that the machines, or the equipment to be sensed or controlled, have a long life span. Most of them can last for more than ten years.