## 4 Experiment Verification
### Security Aspect
#### 4.3.3 Security against Encryption Key Hijacking Attack  
Suppose the proposed DeviceKey\({}_{\text{n-1}}\) key is stolen. Malicious attacker needs to know the value of the Block\({}_{\text{n-1}}\) hash to generate the N\({}^{\text{th}}\) generated DeviceKey\({}_{\text{n}}\). This requires a history of all sensor data sent and received to know the hash value. Alternatively, in order to know the hash value of n\(-\)1 at BlockCondition\({}_{\text{K}}\) =  
Kbyte, respectively. It showed a lower level equivalent to the blockey for \"computational cost/time for encryption key Generation\". In comparison with the related work, the proposed method satisfied the aspects of availability in the low-power wireless communication environment. The \"security against encryption key hijacking attack\" showed a high level equivalent to the blockey as it dynamically generates keys based on the sensor data history (dynamically generated unpredictable sensor values). As shown in Sections 4.3.2 and 4.3.3, it is only possible in cases for malicious attacker make many brute force attacks to know the key generation information or to know the next key generated. It is impossible to find out the key generation information within the next key generated. Therefore, prevention of key generation information exposure and randomness/unpredictability of encryption key were also satisfied. The proposed method satisfied the availability and security of dynamic encryption keys in a low-power radio environment. As shown in the Figure 16, our proposed method is within the scope of research on encryption key. For security in the real Internet of Things environment, access control and authentication on the Internet of Things should be considered [32; 33]. There are also problems to be solved in access control and authentication on the Internet of Things. The study by [PERSON] and [PERSON] [34] to improve the device authentication vulnerability of MQTT protocol, OTP-based authentication protocol using block chain was proposed. The study by [PERSON] et al. [35] decentralized light-weight access control model was proposed to address the issue of scalability of centralized access control. The study by [PERSON] et al. [36] authentication and key management model considering the user's authentication of the device was proposed. Future research \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **OTP (S/Key)** & **[PERSON]–[PERSON]** & **[PERSON]** & **Proposed** \\  & **[PERSON] et al. [29]** & **[PERSON] and [PERSON] [30]** & **[PERSON] [23]** & **Method** \\ \hline \multirow{4}{*}{Availability} & \multicolumn{3}{c}{Encryption Key Generation Communication Method/Steps} \\ \cline{2-4}  & Asynchronous & Synchronous & Asynchronous & Asynchronous \\  & /1 step & /2 steps & /0 step & /1 step \\ \cline{2-4}  & \multicolumn{3}{c}{Encryption Key Recovery Communication Method/Steps} \\ \cline{2-4}  & Synchronous & Synchronous & Synchronous & Asynchronous \\  & /2 steps & /2 steps & /2 steps \\ \cline{2-4}  & \multicolumn{3}{c}{Required Computational Cost/Time for Encryption Key Generation} \\ \cline{2-4}  & Low & High & Low & Low \\ \hline \multirow{4}{*}{Security} & \multicolumn{3}{c}{Security Against Encryption Key Hijacking Attack} \\ \cline{2-4}  & Vulnerable & Average & High & High \\ \cline{2-4}  & \multicolumn{3}{c}{Prevention of Key Generation Information Exposure} \\ \cline{2-4}  & Prevention & Prevention & Prevention & Prevention \\ \cline{2-4}  & \multicolumn{3}{c}{Randomness/Unpredictability of Encryption Key} \\ \cline{2-4}  & Randomness & Randomness & Randomness & Randomness \\  & /Unpredictability & /Unpredictability & /Unpredictability & /Unpredictability \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Comparison table of related studies. Figure 16: Internet of Things security. will refer to the above mentioned studies [34; 35; 36] to study how to extend the dynamic encryption key proposed in the paper to access control and authentication techniques.