## 8 Conclusions  
Vehicle systems have developed significantly and they have recently helped people to drive more comfortably and safely. However, unsolved security problems and large quantities of traffic information have limited the use of vehicle systems. The VCC with message confirmation is the one of solutions to decline burdens of OBU's storage. And VCC helps to use the vast amount of vehicle information easily. In addition, to protect the vehicle information, key agreement and authentication process is also necessary to address malicious attacks, including communication security problems. Additionally, previous studies and the protocol of [PERSON] et al. are not safe for stored values in ideal or realistic TPDs. In this paper, we first showed that protocol of [PERSON] et al. is not secure against session key disclosure and impersonation attacks because of information leaked from a TPD. Their protocol also does not provide privacy of the users and mutual authentication property. Subsequently, we proposed a secure key agreement and authentication protocol for message confirmation in VCC. The proposed protocol withstands various attacks and provides privacy of  
\begin{table}
\begin{tabular}{l c c c} \hline \hline
**Security Properties** & **[PERSON] et al. [13]** & **[PERSON] et al. [16]** & **[PERSON] et al. [4]** & **Ours** \\ \hline Impersonation attack & x & x & o \\ Side channel attack over OBU or TPD & - & x & x & o \\ Trace attack & o & o & o \\ Replay attack & x & o & o \\ Man-in-the-middle attack & x & x & o & o \\ Privacy-preserving & o & o & o & o \\ Mutual authentication & x & x & x & o \\ \hline \hline \end{tabular}  
\end{table}
Table 6: Security Properties.  
\begin{table}
\begin{tabular}{l c c} \hline \hline
**Protocols** & **Execution Energy Consumption** & **Communication Energy Consumption** \\ \hline [PERSON] et al. [13] & 203.978 mJ & 0.239 mJ \\ [PERSON] et al. [16] & 0.774 mJ & 0.181 mJ \\ [PERSON] et al. [4] & 0.305 mJ & 0.225 mJ \\ Ours & 0.024 mJ & 0.181 mJ \\ \hline \hline \end{tabular}
\end{table}
Table 5: Energy consumption.  
users and mutual authentication. We conducted formal security analysis and simulation to prove the security of the proposed protocol. Moreover, we compared computation, communication costs and the security properties with other related protocols. Thus, our proposed protocol is lightweight and suitable for VCC environments. As part of the future, we will put effort into developing a better protocol by applying the developed protocol to the real environment.  
Conceptualization, J.L.; Formal analysis, J.L., S.Y. and M.K.; Software, J.L. and M.K.; Supervision, Y.P.; Validation, S.Y., Y.P., S.L. and B.C.; Writing--original draft, J.L.; Writing--review & edigint, S.Y., M.K., Y.P., S.L. and B.C. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the Institute for Information & communications Technology Promotion (IITP) grant funded by the Korea government(MIST) (No.2018-0-00312, Developing technologies to predict, detect, respond, and automatically diagnose security threats to automotive Ethernet-based vehicle).  
The authors declare no conflict of interest.