# Client-Aware Negotiation for Secure and Efficient Data Transmission
## 4 Result and Analysis
### Encryption Efficiency  
Generally, the power consumption of the processor is related to its running time. In the server cluster, the power consumption can be reduced by shutting down the servers. In WSNs,  
Figure 5: The message exchange procedure of client-aware negotiation based on renegotiation with highest security strength requirement. Figure 6: The message exchange procedure of client-aware negotiation based on renegotiation without the highest security strength requirement. energy consumption can be reduced by using sleeping computing nodes. If data processing and transmission cost can be reduced, then the above two methods can be used to indirectly reduce energy consumption. Therefore, this section indirectly reflects the contribution of this method to energy consumption reduction by measuring data processing and transmission time. Here, the data processing time refers to the time required to prepare the secure data to be sent on the server side. The data processing overhead (\(T_{t}(m)\)) can be divided into three parts, namely asymmetric encryption overhead (\(T_{a}\)), symmetric encryption overhead (\(T_{s}(m)\)), and the rest overhead (\(o\)). Symmetric encryption overhead is proportional to the amount of data transferred (m). The asymmetric encryption overhead is constant. However, the rest overhead can be treated as a fixed value because it is variable, but much smaller than the other two parts. When the overhead of the CAN-SEAT strategy is not taken into account, the expression of \(T_{t}(m)\) is as follows:  
\[T_{t}(m)=o+T_{a}+T_{s}(m) \tag{1}\]  
When the overhead of the CAN-SEAT strategy is taken into account (\(T_{c}(m)\)), the overhead of the second full handshake and renegotiation is considered. However, the overhead of renegotiation is so little that it can be taken into account in the rest overhead. Now, the expression of \(T_{c}(m)\) is as follows:  
\[T_{c}(m)=o+2\times T_{a}+T_{s}(m) \tag{2}\]  
In the process of secure data transmission, the main overhead of the processor comes from asymmetric and symmetric encryption and decryption. We compared the efficiency of encryption and decryption to analyze the contribution of the CAN-SEAT strategy to the actual system. The asymmetric encryption and decryption algorithm was tested using the RSA algorithm, which can be used in key exchange and authentication. In asymmetric encryption, the speed of the encryption is called the signature speed, whereas the speed of the decryption is called the verification speed. The encryption efficiency is described by the number of times the algorithm is executed per second. Symmetric encryption and decryption were tested by AES and ChaCha20-Poly1305, and the encryption efficiency is described by the amount of encrypted data per unit time. As not all machines support AES hardware instructions, the use of AES hardware instructions was analyzed in the experiment. As the block size of symmetric encryption affects the encryption efficiency, we only tested the block size (16 bytes) actually used in OpenSSL, and the experimental results are shown in Figure 7. The signature algorithm (such as SHA) is often used in these algorithms, so we did not test the encryption efficiency of the signature algorithm. The ratio of the lowest security strength to the highest security strength in the experimental results is shown in Table 2. In the experiment, the highest strength key size of the RSA algorithm was 7680 bits, and the lowest was 512 bits. Figure 7a,c,e compares the signature and authentication efficiency of the asymmetric encryption algorithm. As the RSA algorithm key size increases, the encryption efficiency of the asymmetric encryption algorithm decreases. If the CAN-SEAT strategy is adopted, the overhead of the asymmetric encryption can be considerably reduced. For systems with less data transmitted in a fixed time, the time spent for data processing and transmission can be markedly reduced as well.