## 1 Introduction  
As a natural evolution of technologies with an unavoidable link between the digital world and the physical world, the Internet of Things (IoT) is widely adopted in numerous domains [1, 2] such as smart health, smart cities, smart homes, smart grids, smart transportation, and smart shopping. The lives of individuals are significantly impacted by IoT services. Disabled persons can benefit from independence and participation in their social lives thanks to people-centric solutions such as IoT assistance. For example, IoT systems help with in-home physical therapy rehabilitation [3]. IoT technologies also help to reduce dangerous circumstances. For instance, IoT has improved the safety and efficiency of hazardous mining jobs, such as the use of autonomous mining tools that keep employees away from dangerous areas [4]. When combined with warning systems, IoT sensors for temperature, hazardous gas, and smoke can help avoid environmental catastrophes. Several other case studies have also been analyzed in the literature by different researchers [5]. In fact, an increasing demand for smart devices dedicated to consumer use as well as industrial use is observed, fostering the projection of the IoT market to be worth trillions of dollars per year in the short term. These devices are characterized by advanced capabilities allowing the data treatment with the enhancement of processes and provided services. Although there are meaningful benefits of IoT, growing threats and security concerns have appeared and developed with the wide spread of this technology [6]. The heterogeneity of devices, diversity of network protocols and communication technologies contributed to increasing the whole system's vulnerability. According to [7], 70% of Internet-connected gadgets are open to cyberthreats. Among the most popular methods used to attack the IoT environment in recent years, we have cited Distributed Denial of Service (DDoS) [8]. DDoS assaults on IoT gadgets are on the rise and are responsible for several IoT device malfunctions and data leaks. IoT is growing quickly, thus it is time to update pertinent network security measures. Software-Defined Networking (SDN), as a powerful paradigm decoupling control plane from data plane, contributed to addressing security issues, especially in the context of IoT environments [9]. Thus, SDN provides a more flexible, dependable, and secure network. Consequently, many experts and researchers are supporting the combination of the conceptual models of IoT with the innovative network paradigm SDN, and they encourage building a software-defined Internet of Things (SD-IoT) [9; 10; 11] platform as a result of SDN's success in network administration and security maintenance. However, such solutions are built around centralized architectures that present a single point of failure. To overcome the limits of the centralized aspect of SDN, distributed SDN is considered based on multiple controllers. However, the communication between SDN controllers is still challenging and raises security issues. In this context, adopting blockchain on the control plane of SDN architecture can increase the benefit of this paradigm for the management of IoT environment while guaranteeing the security of exchanged information between multiple controllers and domains. Indeed, due to its distributed structure, blockchain is viewed as a potential option to secure IoT [12]. Blockchains [13; 14] are identified as distributed databases that store the data among nodes on a network and guarantee the fidelity and security of data stored on the chain. They are typically used in cases where the data must be trusted without the need for third-party verification. The defining feature of the blockchain is the immutable aspect of the stored data. The latter is stored on the blocks of the chain that are linked together cryptographically, which make it very hard to change without expending considerable resources.