# A Systematic Survey on 5G and 6G Security Considerations, Challenges, Trends, and Research Areas
## 4 Zero Trust Architecture (ZTA)
### Zero Trust Applications in 5G  
IoT: While Zero Trust is desirable for IoT, there are technical challenges that will potentially result in several issues [105]. Network scalability is a major concern with the millions of devices expected to connect through IoT. The sheer number of devices complicates the implementation of policy enforcement. The devices included in IoT infrastructure are simple and resource-constrained and are not appropriate for integrating a robust and secure system. Therefore, this creates an attack vector in the exploitation of inherent weaknesses of the IoT devices [106]. The authors of [105] propose that a policy engine and policy administrator be external to the 5G network and IoT devices, as shown in Figure 9. Through this architecture, no device is implicitly trusted, and all activities and network access must first be reviewed and approved through the Policy Enforcement Point (PEP).  
Smart Grid: Another approach to expanding 5G connectivity is on the power grid. Creating a more connected grid would allow for better maintenance, customer satisfaction, data and analytics, and more. One problem with creating a virtually layered smart grid is the question of reliability and security. A novel approach to connecting power grid devices over 5G using a ZTA is discussed in [107], listing the pros and cons of the proposed Zero Trust method. The author describes the necessity for the network to be under a Zero Trust Architecture due to the mission-critical nature of the smart grid and all of its components.  
MEC: Multi-access Edge Computing provides an opportunity to reduce the overall load on cloud services and latency experienced by the end users by allowing applications to be deployed at the edge of a 5G network. With less computational offloading to cloud services, edge computing would foster better resource efficiency, requiring less bandwidth for each edge device and thereby supporting a larger number of users or end devices. The authors in [108] describe the general security threats to MEC in 5G: infrastructure security, MEC platform (MEP) security, edge UPF (User Plane Function) security, communication security with the 5G core, networking security and MEC application security. Of these listed security threats, MEP, UPF, and MEC application security are particularly important. The approach described in [108] to address this need is a dual-layer ZTA to enforce ongoing  
Figure 9: ZTA overview for IoT.  
authentication with the UE and the CN, along with reinforcement authentication with the edge network, which in the paper's use case scenario is an industrial environment. Through this dual ZTA architecture, a user's derived 'trust value' can be continuously monitored and acted upon, for example, by forcibly de-authenticating the user or device if necessary. Given the vast applications of MEC, additional investigation should be placed on methods that secure the various traffic these devices would produce.  
This concept is expanded with an example architecture for Intelligent ZTA, as described in [14], where the authors introduce an additional Network Exposure Function to the Core Network. This function acts as an intermediary between MEC hosts and the MEC management function, as shown in Figure 10. In this proposed architecture, the MEC host performs internal security scanning through the \"Intelligent Platform Portal\", which is used by the MEC management system's trust evaluation.