## 6 Evaluation and Experimental Results
### Optimization in the Energy Consumption during the Life Cycle of the HIP-Sensor Peers  
It is legitimate that when more security is applied, more energy is required. However, it is an absolute necessity that must be adapted with maximum energy consumption optimization. Cryptography computations consume more energy. Within WSN, all involved nodes perform some cryptographic operations. Since WSN is a limited energy and constraint network, some kinds of cryptographic operations are not appropriate. Consequently, it is meaningful to alleviate the heavy cryptographic operations by proposing either a software solution or a hardware solution or both. This kind of intervention should be studied during the sensor life cycle. The life cycle of a sensor can be defined differently according to the application of WSN, such as industrial WSN, medical WSN, and so forth. In this paper, we propose an authentication solution that may be applied in different constrained environments. Thereby, a sensor can be in two main operational states: sleep state and active state. The sleep mode coincides with the lowest energy consumption of a node because it has no interaction with the network. The active state defines two sub-states: idle mode or data transmission and/or reception data packets mode or generation of data. During the authentication process with LC-DEX, we clearly contribute in minimizing the total energy consumption in both communication and computational sides in an IoT network based on HIP process Indeed, computing and generating the keying material are performed during the active sensor state. As we presented in Section 4.1.2, we contributed to lightening the sensor's charge in the active state. Our new SLA scheme brings two advantages in the sensor energy life cycle, as follows.  
* The delegation of the most heavy cryptographic operation of HIP DEX to the CTTP, has a direct impact in minimizing the computational energy cost of the sensor during the active state and more precisely during the generation data mode;
* The exchanged parameters during the transmission of the R1 packet by the responder and during the transmission of the I2 packet by the responder are minimized in the proposed SLA model (see Section 4.1.2, Figure 7). Hence, we contribute to minimizing the energy consumption during the transmission mode for both the initiator and the responder in the active state.  
Comparing with standard HIP DEX, LC-DEX improve an energy gain about 60% (see Table 14). Consequently, the minimization in the energy cost of the sensor node during the authentication process has a direct impact in the extension of its life. Studying in details the proportion of the energy consumption caused by the HIP DEX authentication process and the tangible extension of the HIP sensor device are with high importance and we are working on it as a future direction.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**HIP Solutions** & \begin{tabular}{c} **Computational Cost** \\ **(mJ)** \\ \end{tabular} & \
\begin{tabular}{c} **Communication** \\ **Cost (mJ)** \\ \end{tabular} &
\begin{tabular}{c} **Total Energetic Cost** \\ **(mJ)** \\ \end{tabular} \\ \hline Standard HIP DEX & 13.365 & 0.329 & **13.694** \\ [PERSON] et al. [20] & 3.43 & 94.55 & **97.98** \\ D-HIP [19] & 15.17 & 86.59 & **101.76** \\ C-HIP [18] & 63.622 & 47.186 & **110.808** \\ CD-HIP [18] & 14.93 & 52.16 & 67.09 \\ Slimfit [17] & 1.286 & not indicated & - \\ [PERSON] et al. [9] & 4.182 & 1.729 & **5.911** \\ LC-DEX & 3.931 & 1.62 & **5.551** \\ \hline \hline \end{tabular}
\end{table}
Table 14: Communication and computational energetic costs of HIP existing solutions.