## 4 Authentication Techniques in 6G Communication
### Token-Based Authentication  
Taken-based authentication schemes emerged as a stateless, scalable, decoupled and transparent secure digital information dissemination framework in B5G as shown in Figure 7. MEC technology is widely incorporated with token-based access control management in next-generation networks. In [141], the authors proposed the JavaScript Object Notation (JSON) web token-based authentication for MEC. The scheme provides compliance with standard requirements for credentials transfer between multiple parties. Token-based authentication and authorization schemes are suitable for 6G-enabled IoTs due to the reduced energy consumption associated with token-based data transfer [142]. The authors in [143] suggested on-chip physically unclonable functions for energy-efficient token-based authentication. The scheme utilizes ECC for compatibility with low-resource IoTs. Due to ease of implementation and functioning of token-based authentication schemes, special mechanisms such as Network Repository Functions (NRF) are employed to generate access tokens for authorization servers in 6G-enabled IoTs. NRF-based authentication works in combination with TLS architecture [144]. In [145], the authors used token-based authentication along with a lightweight security module in 6G-enabled smart city infrastructure. Here, tokens are bound with timespan limits, ensuring limited vulnerability concerning mal-intentioned interference. Figure 7: Token-based authentication in heterogenous 6G networks. \begin{table}
\begin{tabular}{p{42.7 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Ref.** & **Network Model** & **Technique** & **Features** & & **Limitations** \\ \hline
[135] & Wi-Fi authentication & Source hiding with projective hash functions & \(\bullet\) & Rejection to authentication process to any third party & \(\bullet\) & Null values problem Hash collisions \\  & & & & Prevent the location leakages & & \\ \hline
[138] & Mobile Ad Hoc Networks & Bilinear Pairings & \(\bullet\) & Suitable for resource-limited MANET environments & \(\bullet\) & TA dependence SHA-1 Brute force and dictionary attack issues \\ \hline
[139] & Pervasive computing & Bilinear pairings & \(\bullet\) & Formal security proof Identity-based cryptography & \(\bullet\) & SHA-1 Brute force and dictionary attack issue \\  & & & & & \(\bullet\) & Achieves partial deniability only \\ \hline
[140] & Social Networks & Random oracle model & \(\bullet\) & Reduces the computational cost Reduces the length of ciphertext & \(\bullet\) & Specific to awkward conversations over the internet Single logical step & \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Emerging deniable authentication techniques in 6G networks. Token-based authentication provides implementation of QoS-aware 6G-enabled ultra-low latency services in edge communication-based drones, IoTs and health care applications [146]. In [147], the authors suggest a gait information aggregation-based high-coverage authenticated gait diagnosis scheme. However, this scheme suffers issues related to high latency and scalability with respect to mobility requirement of heterogenous IoTs in the 6G network. Token authentication is merging with blockchain and SDN-related unconventional concepts in 6G communication. Blockchain with token-based authentication provides a secure and auditable orchestration mechanism for multi-domain SDN infrastructure in 6G networks [148]. Due to token-based authentication's robust and network-friendly attitude, IEEE 802.11p-based applications are securely migrating to 6G networks [149]. The token-based implementation provides joint authentication and access control in resource-constrained blockchain-enabled IoTs in 6G networks. Token-based authentication mechanisms are vulnerable to prediction and stealing attacks; therefore, it is imperative to formally verify the security strengths of token generation and distribution mechanisms.