### Current Work Contributions  
This paper reviews the latest lightweight security schemes for IoT by stressing the context behind the IoT applications and their priorities in terms of the CIA triad. These will help the reader to understand IoT's multifold security algorithms, especially the lightweight versions of standard ciphers such as Advanced Encryption Standard (AES) and Elliptic Curve Cryptography (ECC). They will be explained in a clear, practical way, through the viewpoint of:  
* The IoT device, its communication protocols, and security features;
* The application domain and how each application adopts the security features.  
In other words, the focus of this review is on the device, its hardware and firmware, the security keys that are programmed in the device, and the network to which it is connected. There are different aspects of _hardware security_ that can be addressed, from the design, manufacturing, and creation of the embedded system with a microcontroller, field programmable gate array (FPGA), and printed circuit board (PCB), as shown in Figure 2. The focus is the customer end of the device creation, as shown on the right side of Figure 2. This is when the node becomes ready to be connected to a network, and be a part of an IoT system.  
Another significant contribution of this work is to review lightweight security protocols based on well-established encryption algorithms, considering different application domains or types of industries. Additionally, this paper considers IoT systems that cover long distances. As a result, the smart devices can be placed in diverse environments. For this reason, the infrastructure and security solutions of a few low-power wide-area networks (LPWA) are explained, in addition to how they are used in different industries around the world.  
Figure 2: The different stages of hardware security.  
In summary, these are our main contributions:
* Apply the CIA triad to explain standard communication protocols as well as lightweight cryptography, in different application domains. The goal is to explain a few protocols in detail while focusing on low-energy and long-range communication technologies.
* Provide a tutorial on IoT lightweight security that is accessible to even non-technical readers. This will illustrate the trade-offs of different protocols for different applications, and provide a good foundation for IoT communications.
* Explain and classify lightweight security approaches for AES and ECC algorithms. They are compared to older security techniques, in terms of primitives such as key sizes, number of encryption cycles, and hardware architectures.
* Bridge the gap between hardware and application developers, telecommunication providers, and customers, on the topic of IoT security's operational priorities and how to apply lightweight security protocols. The main goal is to promote innovation towards the widespread implementation of _open_ IoT systems.  
In 2012, in the early days of IoT, the vision of an _open IoT eco-system_ was introduced. It means a system in which different companies or entities contribute to the system's different parts. It was first described in [13], which is one of the earliest reviews on IoT. It explains the main characteristics of an IoT system, such as device heterogeneity, scalability, and energy-optimized solutions.  
The remainder of this paper is organized as follows. A detailed literature review of IoT and lightweight security is provided in Section 2. Section 3 reviews and explains the communication protocols and security features of three LPWA communication protocols and their security capabilities. Section 4 presents recent studies that make cryptographic protocols more lightweight, mostly at the hardware level. To conclude this paper, Section 5 discusses some lessons learned from this review and future work.