## 8 Conclusions  
The zero-trust concept, since its inception, has already been a successful security model for IT infrastructure and many IT organizations are implementing this model from different vendors to secure their environment and manage their resource access in a controlled manner with the help of dynamic access control policies. With that said, the success of this solution in IT infrastructure can be considered as an example to motivate the security professionals in the smart manufacturing industry to implement the zero-trust security model. The manufacturing industries are still following the traditional perimeter-based security where everything inside the firewall is considered trusted and focuses on production with a very minimum priority on securing the industrial systems. The current security architecture for the manufacturing industries is good enough when there is no or very minimum communication between the industrial systems. However, the Industry 4.0 era has brought in many critical components such as machine learning, Artificial intelligence, cloud computing, etc. to automate manufacturing and business processes. Unfortunately, the more complex the environment is, the more communication between the components and thus, it is more susceptible to cyber-attacks.  
With the introduction of cloud computing, most of the manufacturing resources have been migrated to the cloud reducing their management overhead. This type of hybrid architecture increases the workload of access management because communication between the private infrastructure and the cloud is through the internet. Any hole in the access policies will have a catastrophic impact when exploited by hackers. Although the zero-trust model brings in maximum security in terms of access validation, authentication, and authorization, the major drawback of this is the lack of proof for a successful implementation. There are currently multiple vendors in the market offering zero-trust security; however, it is extremely critical to understand that zero-trust is not just one security product that can be placed in the infrastructure and confirmed to be secured. It is rather a concept that involves multiple aspects of closing down the holes in an environment with the use of different security products such as firewalls, identity & access management platforms, secure remote access solutions, SIEM systems, endpoint security tools, and many others. Depending on the existing architecture of the industry, a solution needs to be designed considering all the possible threats. Only then a zero-trust model can be implemented by combining all the different security solutions to protect the smart manufacturing environment.  
Figure 16: Zero-trust architecture for cloud-hosted data store.  
In the future, this research can be further explored by the addition of new and upcoming security technologies such as secure web access, VPN-less remote access, and cloud security when the industrial infrastructure starts migrating to the cloud.  
Conceptualization, B.P. and M.R.; methodology, B.P.; validation, B.P. and M.R.; formal analysis, B.P.; investigation, B.P. and M.R.; resources, M.R.; writing--original draft preparation, B.P.; writing--review and editing, M.R.; supervision, M.R.; project administration, M.R.; funding acquisition, M.R. All authors have read and agreed to the published version of the manuscript.  
This work has received support from the Higher Education Authority (HEA) under the Human Capital Initiative-Pillar 3 project, Cyberskills.  
Not applicable.  
No new data were created or analyzed in this study. Data sharing is not applicable to this article.  
Thank you to the Department of Electronic and Computer Engineering at the University of Limerick for supporting this work as part of the Masters in Information and Network Security program.  
The authors declare no conflict of interest.