## 4 Research Methodology  
### Experimental Framework  
In network environments, sensitive information must be encrypted before transmission to prevent unauthorized access. In resource-constrained IoT systems, AES encryption has been widely used. While AES provides robust security, the encryption operations are executed by microcontrollers within the devices, which may leak physical signals during the encryption process. These signals could be exploited by attackers to extract the encryption keys, thus compromising the encrypted messages. To counter SCA on IoT devices, we proposed a dynamic key replacement AES encryption algorithm based on the MTD [14] concept. This approach changes the initial encryption key before an SCA can succeed.  
To validate the effectiveness of this defense mechanism, we implemented a wireless communication platform for a smart access control system, which included an RFID-based access control system (Arduino UNO), a Wi-Fi module (ESP8266), and access control software. A laptop executed access control software as client and server in the IoT environment, handling communication between the devices. The smart application system was set up using actual RFID tags, with an RFID reader connected to Arduino UNO. When the RFID tags were read, the data were encrypted by AES and transmitted via the Wi-Fi module to the access control software for decryption.  
Once the encryption and decryption process of the access control data was validated, we conducted an SCA on the system. Using an oscilloscope, we captured electromagnetic radiation emitted during the execution of encryption operations on Arduino UNO, specifically targeting the power consumption data. The oscilloscope used an electromagnetic probe to capture the traces, which were sent to the control computer. These traces were processed by a GPU computing platform using CPA to determine the success of the key extraction by analyzing the number of successfully attacked subkeys. The experimental setup is illustrated in Figure 4.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Ref.** & **Method** & **Key Feature** & **Overhead** & **SCA Resistance** \\ \hline
[3] & Backside Buried & Real-time attack & High & Strong for EM and fault attacks \\
[4] & Metal & detection & (fabrication cost) & Limited by update \\
[4] & Dynamic Key & Periodic key updates & Moderate & frequency \\  & Replacement & using MTD & & High (hardware & Strong for power analysis \\
[27] & Masking & & computations & & \\
[30] & Key Simplification + &
\begin{tabular}{c} Reduced encryption \\ cycles and dynamic \\ key updates \\ \end{tabular} & Low & Resilient to replay attacks \\ \hline \end{tabular}
\end{table}
Table 3: Comparison of the proposed mechanism with selected prior works.  
Once we confirmed the IoT transmission scenario and SCA setup, we modified the AES encryption algorithm to enable dynamic key replacement. To evaluate the efficiency and effectiveness of the key replacement, we performed the key replacement after capturing different amounts of traces and observed the frequency limitations of the key replacement. The configuration of the client, server, and the dynamic key replacement AES design will be discussed detail in the following sections.