## 3 Literature Review
### IoT
#### 3.3.4 Addressing Security Issues with Zero Trust and Network Segmentation  
The authors of [59] researched the usage of blockchain for network segmentation and device identification to implement zero trust principles for IoT devices. They used zero trust to centralise an access control engine for all policies and an agent on all endpoints for policy enforcement. Network segmentation is achieved with a segmentation gateway (SG) and a microcore and perimeter (MCAP) with a switch that connects to SG for centralised management of MCAPs. Any communication between devices is authenticated with the presence of smart contracts in the blockchain nodes of the partners. The authors concluded that multiple security concerns are addressed with their framework, including (a) the concern about device security, which is addressed with MCAPs for IoT devices and security services from the blockchain (partners); and (b) data security, which is enhanced with secure storage that has cryptography controls; and (c) data related to network administration is communicated securely, leading to comprehensive network management. [PERSON] et. al. [12] focused on the difficulty of implementing network segmentation and zero trust policies in 5G-IoT networks due to the presence of millions of devices. The authors studied zero trust architecture and applied it to the IoT environment. They used blockchain enabled authentication leveraging digital signature-based authentication. This resulted in software defined perimeter using the blockchain enabled authentication and zero trust. The authors additionally used PEP, PA and PE to implement access control in IoT devices. The authors concluded that their study introduced zero trust by design for IoT and that device authentication is achieved with blockchain. The authors of [60] proposed an architecture that is zero trust aligned, which uses software defined network to implement micro-segmentation in heterogeneous environments. They defined policies to grant/deny access requests between networks. This was combined with configuration management to generate and distribute certificates that are driven by defined policies. This action ensures that all participating resources have credentials to participate in interactions within networks. The authors concluded that their approach provides flexibility and adaptability to meet the complex requirements of industries without making any modifications to the application layer. The shortcomings of IoT devices in terms of compatibility with 5G network is researched by [61], as 5G offers increased bandwidth, better speed and a higher capacity to handle more devices. The authors study the network slicing that is made possible in 5G networks and the ways of addressing security issues with IoT. Network slicing provides isolation but allows sharing of network functions. However, dynamic allocation is preferred, which addresses the issue. The authors propose zero trust architecture to address the risk of IoT devices being used as attack vector in 5G networks. They propose NIST's [5] zero trust architecture. The zero trust architecture principles that the authors apply to IoT devices are (a) continuous authentication and authorisation of IoT devices, (b) least privilege, (c) micro-segmentation and (d) continuous monitoring. They conclude that zero trust and network slicing present innovative solutions to security issues with IoT using 5G. However, they recommend that similar solutions should be applied to all situations and that organisations should identify the components that are important to them and apply zero trust and network slicing to secure them. Enhancement of zero trust security for IoT with authentication using emerging technologies like blockchain and AI-driven anomaly detection is studied by [62]. The authors summarise the existing authentication methods for IoT with zero trust. The authentication methods include biometric, cryptography, identity and access management--federated and otherwise, blockchain-based and physically unclonable functions (PUFs).