# An Introduction of a Modular Framework for Securing 5G Networks and Beyond
## 3 Proposed Network Service Security (NSS) Framework
### Security Modelling  
This subsection discusses security modelling and a multilayered approach in a modular framework. The secure services model allows the UE to securely access network services from the network and SP. The wireless network is under the control of the 5G network, whose root certificate is kept in the Universal Subscriber Identity Module (USIM) [6]. In the 3 GPP standard, it is mentioned that the UE and ARPF share long-term K by performing a challenge and response, the shared key with other information including identification information is used by the ARPF to generate session keys through collaboration with SEAF and AUSF as explained in [10]. The AUSF is in charge of the network and UE mutual authentication; after initial authentication, the communication link with HN sNB is left open until it is disconnected. If the UE moves to a different gNB, it will require re-authentication and the generated keys and security information might be reused during the handover--which is handled by the ARPF in both the HN and VN, this is out of the scope of this work.  
In this case, the UE obtains access to the services after connecting to the wireless network, 5G is based on a security architecture that is host-centric and the CCN is information-centric; hence, the hybrid approach of the security framework. Normally, the security of the content relies on the encryption of the content object as the producer must register the content object to the database owned by the SP achieving the validation and authentication of the named data object. Multiple methods are used to address the complexity of this system model.  
The security modelling in Figure 3 leverages the security principles by 3 GPP [6] by applying the authentication and authorisation methods that grant the UE service access and permission to engage with other UEs. A multilevel framework is proposed to align  
Figure 2: Unified modular architecture.  
with the network service abstraction and 5G protocol stack [32]. It comprises Network Access Security (NAC), Service Level Security (SLS) and D2D Security (DDS) levels which are parallel with the network service abstraction. It also explores physical layer security (PLS) to highlight the need for security at each level and integrated solutions. This security framework's novelty is mainly on SLS and DDS, as PLS and the NAC have been extensively studied by related work. The PLS and NAC provide security for physical and network access; the SLS provides security for services access; and DDS provides security for D2D services sharing.  
The framework considers the security link between all the security levels, and in addition to the security entities, it is represented as a unified security model. This security framework intends to provide the UE with secure service access and the sharing of these services with UE from another network without losing their initial network access. The security framework intends to provide secure communication and sharing between UEs without the need for HN as the central authority.