## 2 Background
### Related Work  
This section summarises the surveys that have been carried out by authors to apply zero trust (zero trust five-step implementation or otherwise) to smart home environments and IoT. We note that the relevant surveys are very few. The authors of [29] survey the academic and practice-oriented literature to identify gaps that can explain the lack of widespread and holistic understanding of zero trust adoption. They explain that the increasing amount of digitisation and the number of digital devices (IoT, Bring Your Own Devices, etc.) leads to the ineffectiveness of perimeter security. Zero trust offers a novel solution to address the shortcomings of perimeter-based  
Figure 7: Zero Trust Five-Step Implementation Process [7]. security. The authors elaborate zero trust architecture, which consists of Policy Information Point (PIP), policy storage, Policy Enforcement Point (PEP) and zero trust engine. They also elaborate the core principles of zero trust. Their results demonstrate the influence of practice and academia on one another. Their review also demonstrates the implementation of zero trust in specific industries and IoT and considers the literature on architectural variations for IoT networks and smart home networks. Some of the literature demonstrates the applicability of zero trust to smart home infrastructures. They conclude that their survey results indicate unanswered questions that hinder zero trust's widespread adoption but that they have provided a framework to continue research in this space. Zero trust architecture with PEP and zero trust engine as the main components for IoT and smart homes is studied by [29]. The authors discuss zero trust architecture and its common concepts, namely, enhanced governance of authentication systems, software defined perimeter (SDP), reverse proxies, and micro-segmentation. The authors discuss that owing to the innovativeness of zero trust, the existing security controls may not work. They conclude that the current research in zero trust is centred around small networks and is not spread uniformly across industry sectors. They also conclude that architecture for large scale networks is not very well researched and that the disadvantages of zero trust are not well understood. The existing literature on zero trust architecture, including authentication, access control and trust assessment, is surveyed by [30]. A proposal is made for access control for smart homes based on zero trust, which in turn is based on context and continuous authentication. A trust evaluation mechanism uses edge computing for smart products for home IoT. The authors analyse survey results by identifying the advantages and disadvantages of architecture, authentication methods, access control methods and trust assessments. The results demonstrate that (a) user-to-device authentication is verified with biometrics acquired from smart wearables like smart watches and that (b) attribute-based access control provides fine grained access control. The authors conclude that their survey and the results have significance for migrating perimeter-based architectures to zero trust architecture. Zero trust literature on IoT is surveyed by [31] based on a three-point approach and includes the following: (a) the principles of zero trust model; (b) the scope of zero trust in and challenges to address authentication, authorisation, data management, etc. ; and (c) correlation between the latest developments in defence and the creation of resilience-preserving zero-trust models. The authors identify the essential components of zero trust as authentication, network segmentation, authorisation, encryption, network monitoring, PDP, PEP and Policy Administrator (PA) and highlight the difference between traditional security and zero trust. They look at the alignment between zero trust and MITRE ATT&CK framework. They use this alignment to highlight the risks posed by zero trust paradigm for the identified components. They then offer architectures to implement zero trust.