## 4 Authentication Techniques in 6G Communication
### Mutual Authentication  
Lightweight cryptographic solutions are actively researched for mutual authentication and key agreement schemes in resource-constrained IoT devices. In [115], the authors proposed a random HMAC and ECC-based D2D mutual authentication scheme. The scheme guarantees message authorships with 7.7-times-lower delay and reduced complexity. Moreover, the scheme counters several attacks, including free-riding attack. These schemes have gained prominence due to efficient processing and resilient defense against sophisticated attacks such as free-riding attacks. Security policy management is challenging in mobile devices due to dynamic behavior and situational requirements. Therefore, mutual authentication is considered a promising approach for security policy management. In [116], the authors suggested a fingerprint and MAC address-based mutual authentication scheme for a handshake between mobile nodes. The results include strong bit level integrity and improved trust level validation through MATLAB-based simulations. Maritime Transport Systems (MTSs) are incorporated with various mutual authentication schemes to avoid unauthorized vessel location data access. The authors in [117] proposed lightweight mutual authentication in multi-server architecture for MTSs. The scheme provides reduced latencies and shows superior performance in comparison with equivalent designs. However, this scheme is vulnerable to brute force and dictionary \begin{table}
\begin{tabular}{c l l l l l l} \hline \hline
**Ref.** & **Network Model** & \multicolumn{2}{c}{**Technique**} & \multicolumn{2}{c}{**Features**} & \multicolumn{2}{c}{**Limitations**} \\ \hline
[107] & Mobility in terrestrial satellites & Clustering and & \(\bullet\) & Low handover delays & \(\bullet\) & Higher-layer constellation \\  & terrestrial satellites & game-based handover & \(\bullet\) & Low signaling overheads & & design \\  & and 6G terrestrial & decision-based & \(\bullet\) & Fast convergence & \(\bullet\) & Inter-layer management \\  & broadband & lightweight authentication & & & \(\bullet\) & Management structure \\  & & framework & & & & optimization \\ \hline
[37] & Cybertwin edge & Proxy ring signature & \(\bullet\) & Low overhead & \(\bullet\) & Secure migration of \\  & nodes in vehicles & & \(\bullet\) & Low processing requirements & & historical data \\  & to everything & & \(\bullet\) & Low transmission cost & & \\ \hline
[108] & Handover in fog & Cooperative fog nodes & \(\bullet\) & High handover efficiency & \(\bullet\) & Trust management in fog nodes \\  & computing & & \(\bullet\) & Resist known attacks & & \\  & & \(\bullet\) & Low computation & & & \\ \hline
[110] & Mobile edge & Nodes categorization on & \(\bullet\) & Reduce latency up to 5\% & \(\bullet\) & Higher complexity \\  & computing & mobility patterns & \(\bullet\) & Minimal re-authentication latency & \(\bullet\) & Scalability issues \\  & & & \(\bullet\) & Historical data sharing \\ \hline
[114] & Handover in & Multi-connectivity & \(\bullet\) & Handover procedural efficiency & \(\bullet\) & Higher increased initial access \\  & fading signals & architecture & \(\bullet\) & Increased coverage range & \(\bullet\) & Higher base station \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Emerging handover authentication techniques in 6G networks. attacks due to SHA-1. The IoT environment usually has device-to-device communication where the authentication server usually acts as the third party. Batch authentication in 6G-enabled vehicular networks covers wide authentication requirements such as mutual authentication and anonymity. The authors in [118] proposed a secure, anonymous mutual authentication scheme and key agreement in 6G-enabled IoTs. The scheme utilizes the bilinear paring technique to evade message modification. Although the scheme executes with low overhead and reduced computational costs, it is vulnerable to data privacy issues due to a possible compromise of Trust Authority.