## 6 Evaluation of Results  
IoT-Fog-Cloud Architecture with Blockchain-Based Certificate Model versus without Blockchain-Based Certificate Model  
In this subsection, we evaluate the IoT-Fog-Cloud architecture with our blockchain-based certificate model using AWS cloud metrics, as shown in Table 3.  
The first experiment of the IoT-Fog-Cloud architecture was performed using one IoT device. We ran the first experiment twice simultaneously, one without our blockchain-based certificate model and the other with the model. We used two subscribes and two publishes because the IoT device generated two types of data: (A) temperature degree and (B) humidity degree. The results show that the numbers of subscribes and publishes (i.e., subscribe.success and connect.success) for the IoT-Fog-Cloud architecture with and without the blockchain-based certificate model were the same and reflect the defined number of subscribes and publishes for one IoT device. This is because the connection of neither experiment (with versus without the security model) was disconnected and, thus, the subscribe request was not lost. Although the first experiment with the security model had a certificate in the authentication process of the IoT-fog-cloud layers, it did not affect the number of subscribes and publishes. Furthermore, the number of published messages (publishout.success and publishin.success) for the IoT-Fog-Cloud architecture with the blockchain-based certificate model remained the same as that of the architecture without the model. The second and third experiments of the IoT-Fog-Cloud architecture were performed using two and three IoT devices with four and six subscribes and publishes, respectively. The results show that the numbers of subscribes and publishes (i.e., subscribe.success and connect.success) were the same for the IoT-Fog-Cloud architecture with and without the blockchain-based certificate model and reflect the defined number of subscribes and publishes for two or three IoT devices. This is because when the fog device distributed the certificates to the two or three IoT devices, those devices were authenticated simultaneously to the fog device. Therefore, there was no sign of failure in the number of connects and subscribes because the two or three IoT devices remained authenticated to the fog device and started publishing messages. Moreover, the number of published messages (publishout.success and publishin.success) for the IoT-Fog-Cloud architecture with and without the blockchain-based certificate model also remained identical using two or three IoT devices; there was no loss in the number of published messages, as there was no sign of failure in the number of connects and subscribes (connect.success and subscribe.success) because the two or three IoT devices remain authenticated to the fog device and start publishing messages at the same time. Overall, we found that the performance of the IoT-Fog-Cloud architecture with and without the blockchain-based certificate model was the same when using one, two, or three IoT devices. Thus, there was no delay in the number of published messages for the IoT-Fog-Cloud architecture with the blockchain-based certificate model, as shown in Table 3. This is because the first layer of security requirements, authentication, was proposed and added to the IoT-Fog-Cloud architecture, and it did not affect its performance. This means that the IoT-Fog-Cloud architecture had improved performance and security simultaneously.