## 2 Related Work  
This section provides the related literature that has been done in the field of CoAP security, IoT security, various authentication techniques used between IoT devices and agriculture sector. The Hyper Text Transfer Protocol (HTTP) is an application layer protocol used by the World Wide Web to access data on Internet and uses the Representational State Transfer (REST) architecture. The HTTP request and response messages exchange data between HTTP server and client [10]. This protocol is not suitable for IoT and cannot be implemented  
Figure 1: CSFSA architecture. on IoT devices due to computational overhead. As a result, a lightweight and efficient protocol for constrained devices is required. The Internet Engineering Task Force (IETF) Constrained RESTful Environment (CoRE) working group has standardized lightweight application protocol for IoT systems i.e., CoAP. It is a specialized web transfer protocol, specially designed for resource constrained applications. In [11], the authors compared the CoAP and HTTP protocol and evaluated their performances based on energy consumption, battery life and amount of bytes exchanged per session as shown in Table 1.  
Transport Layer Security (TLS) is used for securing HTTP communication over Transmission Control Protocol (TCP). The CoAP communication over User Datagram Protocol (UDP) is secured by using DTLS. However standard DTLS is not suitable for constrained networks due to its computational overhead, complexity and handshake session overhead. In [12], the authors provided brief overview of layered architecture of IoT and security vulnerabilities at each layer. They discussed in details various communication technologies along with their features and limitations which are being used by IoT applications. They also reviewed the existing security mechanisms with their limitations to secure the IoT environment. In [13], the authors presented two-way authentication scheme based on DTLS and RSA cryptographic algorithm. DTLS protocol is implemented in context of system architecture to achieve low overhead and high interoperability. However, due to the deployment of RSA encryption, the computational overhead required by their handshake process requires more energy. [PERSON] et al. [14] presented lightweight secure CoAP i.e., Lithe for securing IoT devices communication. This work provided secure framework by integrating CoAP and DTLS. The standard DTLS is not suitable for constrained devices. The proposed scheme used the DTLS header compression by leveraging 6 LoWPAN standard and significantly reduced the energy consumption. The results showed that compressed DTLS performs better in terms of energy efficiency, network response time, packet size and processing time. In [15], the proposed framework enables the communication between android phones using DTLS secured CoAP. This framework combines other algorithms with DTLS that are not applicable on resource constrained IoT devices. DTLS requires public key cryptography which is a computationally expensive process and a lengthy handshake process [16]. Although there are certain security algorithms which are lightweight and have less overhead such as raw public key, at least 25 bytes per-packet overhead of DTLS takes up one-third of a frame. DTLS heavily hinders the performance in terms of round-trip messages when retrofitted to CoAP [17]. The authors [PERSON] et al. [18], present a scheme for making the implementation secure CoAP lightweight by applying header compression techniques. Although header compression does not offer an improvement in performance because DTLS is computationally intensive. The authors [PERSON] et al. [19] propose a plan that enables the client to assign a certificate path and construction as well as the validation of the certification path to a server. However, this protocol is expected to be used over HTTP. This protocol relies on third-party instead of communication parties and adds a heavy communication overhead. In [13], a framework for the end-to-end security of IoT has been presented.