Zero trust is a cyber security approach in which no user, device, system or network connection is trusted automatically. This matters because operational technology increasingly connects with IT networks, cloud platforms, remote engineers and third-party suppliers. The aim is not to block essential work. It is to give the right person or service access to the right asset, at the right time and under the right controls.
What Is Zero Trust?
Zero trust checks each access request instead of relying on a trusted network location. Before granting access, an organisation should confirm who or what is making the request, whether the device is approved and which resource is needed.
Permission should be limited to the task. An engineer may need access to one programmable logic controller, human-machine interface or engineering workstation, but not the wider operational technology network. Checks should continue during the session so permissions can be changed if the risk increases.
Why Traditional Network Trust Creates Risk
Older models often treat users and devices inside the network as trusted. In industry, this can combine with flat networks, shared engineering accounts, broad virtual private network access and permanent supplier connections.
If one account or device is compromised, an attacker may be able to move between systems. Legacy PLCs and HMIs add risk because they may have limited security functions and restricted patching windows. Controls must reduce unnecessary access without affecting production continuity or safety.
Core Zero Trust Principles
A practical zero trust programme uses five connected controls.
Verify Identity
Every user, service and device should have a clear identity. Named accounts and multi-factor authentication make access easier to control and investigate.
Check Device Trust
Access decisions should consider whether a device is known, approved, maintained and suitable for the environment.
Apply Least Privilege
Users and systems should receive only the permissions needed for a defined task. Access should end when the task, role or contract ends.
Segment Access
Connections should be limited to specific zones, systems, applications or protocols, reducing unnecessary communication and lateral movement.
Monitor Continuously
Access activity should be logged and reviewed to identify unusual behaviour, unknown devices or attempts to reach unapproved systems.
Zero Trust In OT And Industrial Control Systems
Applying zero trust in operational technology requires care. Industrial environments may include PLCs, supervisory control and data acquisition systems, historians, gateways, engineering workstations and vendor-maintained machines. Availability, safety and predictable operation remain essential.
A control used in office IT may not suit a production line without testing. Older assets may not support modern authentication or endpoint software. The design should reflect asset criticality, production needs and existing architecture. Industrial firewalls, controlled gateways and managed access paths can protect systems that cannot support stronger functions directly.
Secure Remote Access For Industrial Teams
Remote access helps engineers, original equipment manufacturers and system integrators diagnose faults and support machines. However, broad access can expose more of the OT environment than the user needs.
A zero trust model should verify each remote user and device, restrict the connection to the required machine or application, control session duration and record activity. Permissions should be removed when no longer required.
M.A.C Solutions supports organisations reviewing secure remote access. TXOne Networks solutions can also support asset protection, network controls and industrial visibility.
Segmentation And Boundary Protection
Zero trust and network segmentation work together. Segmentation separates networks and assets into controlled zones, while access policies decide which users, devices and services can communicate with each zone.
This may include separating IT and OT, creating an industrial demilitarised zone, restricting access to critical PLC networks and controlling traffic between production cells.
Organisations reviewing OT cyber security should treat identity, access, segmentation and monitoring as one strategy.
Supporting Wider Industrial Cyber Security
Access controls work best alongside wider security measures. Asset visibility and a network audit help teams understand devices, users, communication paths and remote connections before applying new policies.
AMDT Octoplant can support automated backups, version management and change visibility. Dedicated USB cyber security measures can help check files and contractor media before they reach sensitive systems. Recovery plans should explain how access will be revoked, assets isolated and known-good configurations restored.
How To Start A Zero Trust Journey
Moving to zero trust should be a phased programme rather than a complete technology replacement:
- Identify critical assets, users, services and data.
- Review local, remote and supplier access routes.
- Map communication between IT, OT and third parties.
- Remove unnecessary accounts, permissions and trust relationships.
- Apply least-privilege access to priority systems.
- Segment critical networks and control boundary traffic.
- Monitor users, devices, services and access requests.
- Review backup, recovery and isolation procedures.
- Improve controls in manageable stages.
Many organisations will retain some perimeter controls while older equipment is updated. The priority is to reduce risk without causing avoidable disruption.
Frequently Asked Questions
What Is Zero Trust?
Zero trust removes automatic trust from users, devices and network locations. Each request should be verified, authorised and limited to the resources required.
How Is It Different From A VPN?
A VPN creates an encrypted connection but may provide broad network access. This model limits access to specific resources and continues checking identity and device condition.
Is Zero Trust Suitable For OT Environments?
Yes, but controls must account for legacy assets, maintenance windows, safety requirements and production constraints.
Does It Replace Network Segmentation?
No. The model controls access to resources, while segmentation limits communication between networks and zones. They work together.
How Should Industrial Teams Begin?
Identify critical assets, users, services and access paths. Remove unnecessary permissions, prioritise high-risk systems and introduce controls in phases.
How M.A.C Solutions Can Help
M.A.C Solutions has more than 25 years of experience supporting industrial IT and OT environments. We help manufacturers, original equipment manufacturers and system integrators review access, segmentation, remote connectivity and legacy assets.
Our teams also support wider industrial cyber security services, helping organisations select practical controls that reflect production priorities and long-term support requirements. Organisations exploring zero trust for industrial environments can speak with our team about a phased approach suited to their architecture.
