## 2 Background
### Related Work
The authors conclude that the survey reveals a number of zero trust systems that are cloud based which are implemented in centralised mode and in edge-based decentralised mode. They also conclude that zero trust is likely to reduce zero-day attacks and reduce the attack surface. The authors of [32] survey access control solutions for IoT, including ones based onzero trust, which include PEP, Policy Definition Point (PDP) and PIPs as components of attribute-based access control (ABAC), which are also the components of zero trust access architecture as documented by NIST SP 800-207 [5]. They introduce various access control models, both centralised and distributed. The authors mention that due to the large-scale use cases of IoT network, access control between devices for which a distributed model works best is a critical security control. Blockchain is a suitable distributed technology that addresses this requirement. They conclude that their survey is expected to facilitate effective guidance to enable understanding of access control solutions. They further conclude that the categorisation of access control models and approaches is important to industries and organisations, as it helps in selecting the right approaches and models for their needs. [PERSON], [PERSON] et.al. [33] survey the literature on zero trust architecture framework, access control, evaluation methods for access control and trusted authentication. They compare traditional security and zero trust security paradigms and summarise key strengths and shortcomings of zero trust network approaches. Their literature review discusses how perimeter-based security is no longer trusted because of the prevalence of cloud applications and IoT networks. They design a taxonomy of zero trust features and compare zero trust cloud networking approaches. Their study reveals the importance of including zero trust principles in 5G/6G networks, as IoT devices interact among themselves while delivering services. They compare zero trust techniques used by IoT platform. The authors conclude that their survey emphasises the necessity of continuous authentication and authorisation based on context, behaviour and perceived threats, which are the tenets of zero trust. The authors of [34] survey the literature that discusses digital signatures used in IoT environments. Digital signatures are used to address integrity, non-repudiation and authenticity to secure devices and data. Because of the heterogeneity of IoT devices, their small footprints and the limited compute power of IoT applications, they cannot consume more features than that supported by modern digital signatures. Working in zero-trust environments requires a Trusted Third Party (TTP) for key distribution, which is difficult for some applications and platforms. The authors survey digital signatures that have been recently designed and that address the challenges of IoT, which are (a) working in zero trust environment (b) privacy preserving and (c) functionality. They analyse the survey results to show that lightweight scenarios can use Keyless Digital Signature (KDS), Randomizable Digital Signature (RDS) and Double Authentication Preventing Digital Signature (DAPS) schemes, some of which can be implemented without TTP. These schemes also address insider attacks from reliably registered IoT entities but which try to maliciously access and compromise security and/or privacy. They compare advanced digital signatures that address zero trust management. They conclude that five of their selected digital signature schemes address security and privacy concerns while being compatible in zero trust environments. [PERSON] et.al. [35] survey the literature studying the various types of applications of IoT in cybersecurity, for example, using IoT devices on the edge network to detect threats and using IoT equipment to respond automatically to breaches by blocking access to network or systems.