## 3 Proposed Model and Methodology  
### IoT System Architecture  
In the context in which the Internet of Things (IoT) is becoming more and more ubiquitous in various fields, ensuring the effective protection of data transmitted between IoT devices has become a major priority. To meet the security challenges imposed by the limited resources of devices and the complexity of distributed networks, we propose a layered architecture, which includes three distinct levels of security. Each level is adapted to the technical specificities of the nodes in the network and their role, so that the entire system benefits from robust, scalable and efficient protection. At the base of the IoT architecture are the sensor nodes, which have the role of collecting raw data from the environment, such as temperature, humidity, pressure or even air pollution. These devices are usually extremely small and have limited resources,both in terms of memory, processing power and battery life. Therefore, securing the communications of these devices is a considerable challenge. Considering the limitations of the hardware, the encryption algorithms used to protect the data are built on the basis of elliptic curve cryptography (ECC). This is a very efficient encryption method that offers a high level of security using keys significantly smaller than traditional RSA-based cryptography. Thus, ECC allows a compromise between security and resource consumption, which makes it ideal for IoT environments, where every bit of energy and every memory unit counts. Regarding key management, IoT nodes use deterministic pseudo-random number generators, which allow the creation of private keys in an efficient way, without requiring expensive additional hardware. This aspect significantly contributes to reducing the costs of implementing and maintaining IoT networks, making these solutions more accessible and scalable. At the intermediate level of the architecture are the gateways, which play an essential role in centralizing and processing the data received from the sensory nodes. These devices have a higher processing and storage capacity compared to the sensor nodes, which is why they are able to implement more complex encryption algorithms and exchange cryptographic keys between the nodes and the central server. The gateways filter and pre-process the data collected from the sensors, ensuring that only the relevant information is transmitted further, thus reducing the required bandwidth and improving the efficiency of the system. Besides this data centralization functionality, gateways play an active role in monitoring local network security. They are equipped with specialized software that allows the detection of behavioral anomalies, such as attack attempts or unusual behaviors that may signal a security breach. The detection and signaling of these anomalies are essential for the prevention and rapid response to possible attacks. Also, gateways are often able to analyze data flows in a more detailed way, using machine learning or artificial intelligence techniques to improve the identification of attacks and other malicious behavior. The last level of the architecture is constituted by the central server or the cloud infrastructure, which plays the main role in the coordination of the entire network and in the implementation of advanced security measures. These servers are able to run high-performance encryption algorithms and store data long-term. They are equipped to manage large volumes of data and to perform complex analyzes on them, to determine the risks associated with each node in the network and to update security policies in real time. An important aspect of central servers is that they are responsible for large-scale cryptographic key management. They generate, revoke and synchronize the cryptographic keys used by IoT nodes and gateways, ensuring that all devices on the network benefit from real-time protection.