# Quantum Key Distribution for 5G Networks: A Review, State of Art and Future Directions
## 4 Quantum Key Distribution Categories
### QKD Based on Multiphoton
The Multiphoton QKD based on double-lock encryption has been introduced to overcome the weaknesses of a single photon and its variants [118]. The random secret key needs to be travel in a multi-stages step to make the transmission channel more secure and making the eavesdropper difficult to guess the state of the qubits. Same as BB84, the procedure of Error Concealment and Privacy Amplification is subsequently performed to minimize the knowledge of Eve towards the information. This protocol has significant benefits in increasing the distance's limit and provides higher SKR than the existing single-photon QKD. However, although any QKD protocols provide unconditional security, they still need an authentication procedure before the communication due to the key needs to be distributed to the right communication parties [119; 120]. Therefore, implementing an  
Figure 4: Quantum Communication using the multiphoton approach. effective authentication procedure using a secure shared authentication key for multiphoton has been introduced to overcome the issue as mentioned earlier [121]. The advantages of the multiphoton approach are that it can solve the intricated heterodyne and homodyne detection and noise-sensitive problem. Thus, a detector with less efficiency is more appropriate when using multiphoton protocol. Furthermore, multiphoton implementation using multiple stages is designed to solve the security problem such as man-in-the-middle attack, photon splitting number attack, and Trojan Horse attack that occurred in the single-photon protocol. Currently, there is no involvement of the public channel in the multiphoton protocol as the exchanging keys process, and the entire procedure is performed only through a quantum channel. The multiphoton protocol is initially designed for Quantum Secure Direct Communication (QSDC), where the protocol eliminates the key distribution process and directly shares the message using quantum channel [122; 123]. Recently, the researchers have hotly discussed the works on improving QSDC. The quantum-memory-free version of the efficient-QSDC protocol is based on original work [123] was proposed by [PERSON] and his collaborators [124]. As a result, the protocol is robust to individual attacks and produces high communication efficiency. Meanwhile, QSDC can be made into measurement-device-independent to create high communication distance [125]. QSDC can also be implemented with single-photon measurement to increase the secrecy of the protocol [126]. Furthermore, the two-step transmission can be further simplified by using hyperentanglement in one round. As a result, this protocol can improve transmission efficiency compared to standard quantum communication [127]. Furthermore, the concept of multiphoton QKD is to perform a key exchanging process by utilizing the polarization rotational in the multi-stages protocol [118; 128]. Furthermore, multiphoton QKD is easily implemented in the administered network infrastructure. Multiphoton QKD are also not required to produce the same polarization states as in the BB84 protocol due to the generation of an arbitrary polarization state that can avoid the man-in-the-middle attack. Despite multiphoton successes, determining the number of stages and the optimal mean photon numbers to ensure that the protocols function correctly during operations remain critical concerns. Therefore, the works on enhanced multiphoton have been resolved the issue of increasing source redundancy [129], improved the authentication procedures [121] and improved the achievable secret key rate as well as distance coverage [130]. With the emergence of quantum technology, the chip-based QKD is introduced [131]. Chip-based technology can offer small size and low energy consumption for a low cost. Table 2 shows the QKD protocol based on [PERSON]'s Uncertainty Principles.