## 4 Authentication Techniques in 6G Communication
### Handover Authentication  
With the exponential expansion in mobile devices and advancement in network technology, cellular data traffic has increased. Secure and seamless mobility of devices in a cellular network primarily depends on authentication during the handover process. Due to limited processing power and exposed wireless links [105], it is extremely challenging to design an appropriate handover authentication protocol [106]. An efficient and dependable handover authentication scheme needs to be developed for guaranteed security in the massively mobile and integrated paradigm of next-generation networks. Handover authentication is visualized as a significant security- and mobility-related proper functionality in unconventional network implementations such as terrestrial satellites. The 6G network is envisioned as an integrated holistic network capable of handling terrestrial satellite network applications. The handover authentication is a challenging problem due to multi-domain scenarios as shown in Figure 5. The authors in [107] proposed a lightweight clustering and game-based handover decision framework with authenticated ground mobility management configurations in 6G-integrated mega satellite constellations. This provides reduced handover delays, signaling overheads and fast convergence. However, this does not cover issues such as handover in higher-layer constellations, inter-layer management and management structure optimization.  
Similarly, the authors in [37] proposed a handover authentication scheme for 6G Cybertwin between mobile vehicles and edge nodes. This scheme uses a proxy-based ring  
Figure 5: Handover authentication in 6G paradigm.  
signature technique for handover authentication. Blockchain-based handover authentication is visualized as a potential candidate for 6G secure handover. The authors in [108] suggested an efficient, lightweight cryptography-based handover authentication scheme for the fog computing environment. Mobile edge computing reduces handover authentication latency due to mobility pattern traceable schemes [109]. In [110], the authors provide categorization on the basis of mobility pattern to reduce handover latencies and reauthentication delays. However, the scheme lacks consideration of complexity, compatibility and scalability issues. 6G networking concepts are evolving toward a heterogeneous integrated environment with massive mobile entities such as vehicles, drones, UAVs, etc. [111]. Handover management is emerging as a critical area in researching and implementing network domains. Drones and UAVs are mobile in 3D space, due to which handover authentication becomes much more challenging [112]. Poor propagation, shadowing and fading effects are seen as millimeter wave-based contributors for increased complexity in challenges related to the handover mechanism in 6G [113]. The authors in [114] proposed multi-connectivity architecture for improved handover procedural efficiency and coverage range in fading signals. Massively dynamic and multilayer architectures lead mobile devices to frequent handovers in 6G networks. Table 6 summarizes this analysis on handover authentication techniques for 6G mobile networks.