# Improved Chaff-Based CMIX for Solving Location Privacy Issues in VANETs
## 8 Conclusions  
In this paper, we investigated Christian et al.'s Chaff-based CMIX scheme [14] that concentrated on low-density situations as essential and possible daily scenarios. However, their scheme is not sound in achieving security and privacy. Furthermore, the scheme cannot resist linkability attacks in vehicles communication, CF malicious injections, which affect safety applications, and the leakage of mix-zones' symmetric keys to unauthorised vehicles. To overcome the weaknesses of Christian et al.'s scheme, we utilised a version of [15] by using certificates instead of IDs to accomplish mutual authentication to enhance the security and privacy of the legitimate entities. Furthermore, we accomplish unlinkability by preventing low-density exploitation via increasing the density securely and by generating unlinkable pseudo-identities for each message based on an unexampled secret authentication key. Moreover, we increase the efficiency of the Chaff messages by using ACF to overcome the CF disadvantages. To prevent malicious injection in ACFs, the \(RSU\) signs the new fingerprinted Chaff pseudo-identities and keeps the distribution for \(RSU\)s only. We apply a Diffie-Hellman key exchange method after the mutual authentication to prevent unauthorised vehicles from symmetric key access to mitigate any leakage of  
\begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline  & **Our Scheme** & [14] & [21] & [13] & [15] & [10] & [35] \\ \hline Sufficient density & ✓ & ✓ & \(\times\) & \(\times\) & \(\times\) & \(\times\) & \(\times\) \\ Unlinkability & ✓ & \(\times\) & \(\times\) & \(\times\) & ✓ & ✓ & ✓ \\ Mutual authentication & ✓ & \(\times\) & \(\times\) & \(\times\) & ✓ & \(\times\) & \(\times\) \\ Non-repudiation & ✓ & \(\times\) & ✓ & ✓ & \(\times\) & ✓ & \(\times\) \\ Cryptographic Mix-zone & ✓ & ✓ & \(\times\) & ✓ & \(\times\) & \(\times\) & \(\times\) \\ Outside mix-zone privacy & ✓ & \(\times\) & \(\times\) & \(\times\) & \(\times\) & \(\times\) & \(\times\) \\ No interference with safety applications & ✓ & \(\times\) & ✓ & ✓ & \(\times\) & \(\times\) & \(\times\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: A Comparison of the proposed and existing schemes.  
the mix-zone symmetric key. In future work, we believe that we have to evaluate our scheme and provide performance evaluation results to make the work more convincing. In addition, we will investigate our scheme efficiency in tunnels and confined area.  
[PERSON]M. is the principal author of this article as part of his PhD thesis, A.H.A.-B., M.S.K. were involved in planning and supervised the work. M.S.A.-M. The specific contribution made by each author are as follows: Conceptualization, M.S.A.-M., A.H.A.-B. and M.S.K.; methodology, M.S.A.-M.; validation, M.S.A.-M., A.H.A.-B. and M.S.K.; formal analysis, M.S.A.-M.; investigation, M.S.A.-M.; M.S.A.-M.; writing--original draft preparation, M.S.A.-M.; writing--review and editing, M.S.A.-M., A.H.A.-B. and M.S.K.; visualization, M.S.A.-M.; supervision, A.H.A.-B., M.S.K. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The authors declare no conflict of interest.