# Quantum Key Distribution for 5G Networks: A Review, State of Art and Future Directions
## 2 Security Challenges in 5G Network
### Authentication  
Authentication is a crucial security aspect in every communication channel to validate the users' identity. Every generation of mobile communication has developed various methods and frameworks for the authentication process. Consequently, this section focuses on the authentication scheme designed by 3 rd Generation Partnership Project (3 GPP) specifically for the 5G communication system. Generally, there are two categories of authentication that is primary and secondary. 3 GPP has released the evaluation standard of 5G Phase 1 in the 3 GPP Release 15. Network and device mutual authentication that supports both 4G and 5G is provided in the primary authentication. However, primary authentication also has some limitations because of the evolved 5G environment. Home automation authentication system manages the information and device authentication. 5G Authentication and Key Agreement (5G-AKA) and Extensible Authentication Protocol (EAP-AKA) are two primary mutual authentication techniques in 5G Phase 1. EAP-based authentication is allowed for a particular scenario, such as private networks. Since primary authentication is not dependent on the Radio Access Technology (RAT), it can be used with non-3 GPP technologies. Secondary authentication is used to authenticate data networks outside of a mobile network operator's area. EAP based authentication and associated credentials methods can be applied to this method. Supplying key material to be used between the network and UE along with mutual authentication can be achieved using primary authentication and key management. The serving network-specific anchor key (KSEAF) are provided by key agreement procedures and the primary authentication. In the serving network, KSEAF is sent to Security Anchor Function (SEAF) by the home network's Authentication Server Function (AUSF). Based on technical specifications published by ETSI and 3 GPP, AUSF works as a Network Function (NF) Service Provider that offers UE authentication to the requester NF. Furthermore, AUSF gives the NF service customer access to the Access and Mobility Management Function(AMF) for UE authentication. During the authentication process, NF supplies AUSF with the UE's identification and serving network name. For EAP-based authentication or 5G-AKA, AUSF will utilize the information supplied by AMF. Various research on security threats and security mechanisms for heterogenous 5G has been conducted for different scenarios and threats. Formal analysis on the 5G-AKA authentication protocol is shown in [19], where the security goals weaknesses are highlighted, and the requirements of 3 GPP standards for 5G networks are discussed. [PERSON] et al. proposed a public-key infrastructure (PKI) based authentication scheme deployed above the asymmetric cryptography to authenticate the base station in the 5G network. Moreover, the analysis of 5G-AKA is presented by authors in [20]. The research shows that the 5G-AKA depends on the core network. [PERSON] et al. discussed the challenges and threat model for 5G-AKA protocols, where the author demonstrated the logical vulnerabilities that require dedicated fixes [21]. [PERSON] et al. investigated the vulnerabilities of 4G and 5G-AKA protocol to understand the weaknesses of Authentication Authorization and Accounting (AAA) [22]. Authors in [23] presented the 3 GPP-AKA protocol with perfect forward secrecy for the session key. The proposed protocol focused on the compatibility of perfect forward secrecy with the current Universal Subscriber Identity Module (USIM) 5G-AKA protocol. Moreover, [PERSON] in [24] offers a group-based authentication threat model for a heterogeneous 5G network. In [25], the authors studied the 5G-AKA protocol for the 5G mobile communication network. The proposed protocol utilized asymmetric randomized encryption to provide better privacy and secure communication. Furthermore, the proposed protocol shows that all possible attack against 5G-AKA privacy still applies except the IMSI-catcher attack.