## 6 Discussion
### Security of the 5 GAKA-LCCO Protocol
Additionally, the protocol in [26] removes the synchronization failure procedure and the MAC failure procedure, preventing the location privacy of the UE from being compromised and defending against those attacks based on MAC failure. Similarly, \(MAC_{ARPF}\) is also included in \(AUTH_{SEAF}\) of the second received message of the UE, but it does not contain \(SEAF_{ID}\), where \(MAC_{ARPF}\) is a MAC of the ARPF and \(SEAF_{ID}\) is the identity of the SEAF (i.e., \(SNN\) mentioned above). This means that the UE cannot authenticate the SN being authenticated by the HN, meaning that mutual authentication between the UE and the SN cannot be established and \(K_{SEAF}\) \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Security Issues** & **5G AKA** & **[23]** & **[24]** & **[26]** & **[28]** & **5 GAKA-LCCO** \\ \hline \(SUCI\) can be replayed without & & Yes & No & Yes & No & No \\ being found & Yes & Yes & Yes & Yes & No & No \\ Mutual authentication cannot be established & & Yes & Yes & Yes & No & No \\ between the UE and the SN & & Yes & Yes & Yes & No & No \\ \(K_{SEAF}\) cannot be agreed among & & Yes & Yes & Yes & No & No \\ the UE, he SN and the HN & & & & & & \\ The location privacy of the UE & & & No & No & No & No \\ can be compromised & & Yes & Yes & Yes & Yes & No \\ Dos attacks against the SN & & Yes & Yes & Yes & Yes & No \\ can be formed & & Yes & Yes & Yes & Yes & No \\ Attacks based on MAC failure & & Yes & Yes & No & No & No \\ can be performed & & & & & & \\ Perfect forward secrecy & & Yes & Yes & Yes & No & No \\ cannot be provided & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparative analysis between the 5 GAKA-LCCO protocol and the recently improved 5G AKA protocols [23; 24; 26; 28] regarding the shortcomings of the latest version of the 5G AKA protocol. cannot reach an agreement. In addition, \(RAND_{SEAF}\) is included in \(RAND^{\prime}{}_{UE}\) of the second received message of the SEAF, \(HXRES^{*}\) of the third received message of the SEAF, and \(RES^{*}\) of the fourth received message of the SEAF, but the SEAF does not verify these three fields, so DoS attacks against the SN can be formed, where \(RAND^{\prime}{}_{UE}\) is calculated based on \(RAND_{UE}\) and \(RAND_{SEAF}\) (i.e., the challenges of the UE and the SEAF, respectively). Because \(K_{AUSF}\) and \(K_{SEAF}\) can be calculated when \(K\) is leaked, PFS cannot be provided. In [28], \(K\) is replaced with \(BK=KDF(K,x\cdot y\cdot G||SNN)\) on both the UE and the HN, so \(AUTN\) must contain the challenge of the UE (i.e., \(x\)), which is included in \(SUCI\) generated by the UE. Hence, the UE can find whether \(SUCI\) is replayed. However, both the SN and the HN cannot find whether \(SUCI\) is replayed, resulting in DoS attacks against both the SN and the HN. Because the mutual authentication and injection agreement among the UE, SN, and HN are established, \(K_{SEAF}\) can reach an agreement among the UE, SN, and HN. Because \(AUTN\) contains the challenge of the UE (i.e., \(x\)), the first received message of the UE (including \(AUTN\)) cannot be a replayed message, preventing the location privacy of the UE from being compromised. In addition, the UE directly discards the first received message without responding to a \"MAC failure\" indication when \(XMAC\) and \(MAC\) are different, defending against those attacks based on MAC failure. Because \(K_{AUSF}\) and \(K_{SEAF}\) are generated based on \(BK\), this provides PFS based on the Diffie-Hellman exchange. Therefore, our proposed 5 GAKA-LCCO protocol is better than the recently improved 5G AKA protocols in overcoming the shortcomings of the latest version of the 5G AKA protocol.