OT Digitalization Simplified: SINEC Secure Connect

KEYWORDS: SINEC Secure Connect, OT Secure Remote Access, Industrial Zero Trust Network, Brownfield OT Digitalization, NIS2, Cybersecurity Compliance, Cyber Resilience Act, SBOM

Overview

Most manufacturers operate brownfield facilities with automation equipment that remains in service for decades. As organizations pursue digitalization initiatives such as remote diagnostics, predictive maintenance, cloud connectivity, and AI-enabled applications, these legacy environments face growing cybersecurity challenges. At the same time, regulatory requirements such as NIS2 and the Cyber Resilience Act are increasing pressure on industrial operators to improve security, auditability, and operational resilience.

Traditional approaches to remote connectivity, particularly network-level VPNs, can introduce security risks, operational complexity, and scalability limitations in brownfield environments. Zero Trust architectures based on secure overlay networks can help industrial organizations modernize access, reduce cyber risk, and support digital transformation without costly network redesigns. This ARC View examines how industrial operators can securely digitalize legacy OT environments while meeting emerging cybersecurity and compliance requirements, using Siemens SINEC Secure Connect as one example of an approach purpose-built for these challenges.

Modern Zero Trust connectivity architectures can help industrial organizations reduce cyber risk, digitalize legacy OT assets, and support NIS2 and Cyber Resilience Act compliance.
 

Key Takeaways

• Regulatory Requirements (NIS2): In 2026, enforcement becomes real. Secure remote access and complete, audit ready logging for brownfield systems are immediate operational and compliance obligations.
• Weaknesses of Traditional VPNs: Legacy VPNs don’t fit modern OT: they grant too much trust, enable lateral movement, require risky inbound firewall rules, and break down with overlapping IP ranges.
• Zero Trust via Overlay Networks: SINEC Secure Connect addresses these challenges with a virtualized overlay, separated control and data planes, granular micro-segmentation, outbound-only connections, and no costly network rebuilds. The result is a fully scalable migration path and stronger network resilience.

Brownfield OT Connectivity Challenges

Modern industrial plants are rarely greenfield facilities. Most manufacturing capacity resides in brownfield operations with legacy PLCs, HMIs, drives, and SCADA systems that remain in service for 15 to 30 years. While highly reliable, these assets were designed for isolated industrial networks and generally lack modern security capabilities such as encryption, authentication, and granular access controls.

As companies connect these systems to cloud platforms, Industrial IoT applications, and remote service providers, they expose legacy protocols and architectures that were never designed for external connectivity. Industrial organizations must also contend with increasingly sophisticated cyber threats and stricter regulations, including NIS2 and the Cyber Resilience Act.

Several technical obstacles complicate brownfield digitalization. Existing plants often lack practical network segmentation, making adoption of Purdue Model or IEC 62443 architectures difficult without extensive downtime. Legacy equipment from multiple OEMs frequently creates IP address conflicts that require complex workarounds. Traditional VPN-based remote access can provide overly broad network access, increase the risk of lateral threat movement, require inbound firewall openings, and create significant administrative overhead.

To address these challenges without costly rip-and-replace projects, industrial operators are increasingly adopting OT security solutions that enable secure connectivity, regulatory compliance, and operational continuity.

One Solution: SINEC Secure Connect

Siemens addresses these legacy connectivity vulnerabilities with SINEC Secure Connect, a cloud-managed Zero Trust platform engineered to secure and simplify remote access to machines, plants, and industrial control systems. The platform establishes a secure virtual overlay network above the existing OT infrastructure, enabling secure communications without traditional VPNs.

At the core of SINEC Secure Connect is an architecture that separates the control plane from the data plane. The Controller acts as the central management engine, authenticating identities, managing security policies, and distributing certificates via a built-in public key infrastructure, while ensuring that no production payload or process data passes through it. The data plane runs directly between local edge gateways and end-user devices using end-to-end encrypted, identity-verified connections.

Rather than relying on classic network routing or complex IPSec tunnels, SINEC Secure Connect virtualizes network communication. Authorized connections are initiated as outbound-only requests from the shop floor, eliminating inbound firewall rules and rendering the local OT network invisible to external scanners. Access is enforced through micro-segmentation and the principle of least privilege, restricting user communication to specific ports or devices and preventing lateral threat movement. Because the overlay network virtualizes connections, operators can bridge overlapping IP subnets without reconfiguring existing automation devices.

Benefits for Brownfield IoT Integration

This architecture delivers significant benefits for brownfield IoT integration by enabling secure digitalization without disrupting existing assets. First, it simplifies remote servicing by replacing slow, manual, or insecure workflows with standardized, zero-configuration remote access. This accelerates troubleshooting and remote software updates, reducing mean time to repair.

Second, it enhances the overall security posture and aligns operations with IEC 62443 security standards. By logging all access attempts and session details, the centralized Controller provides clear audit trails for regulatory compliance while eliminating unauthorized shadow OT configurations.

Third, the platform integrates seamlessly with existing infrastructure as a non-disruptive, additive solution that does not require a network overhaul. Gateways can run on standard industrial PCs or as software on existing edge devices, operating strictly at the management and diagnostic level so they do not interfere with real-time, deterministic control communications.

Finally, it provides a secure foundation for advanced IoT services by establishing robust machine-to-cloud data pipelines that enable predictive analytics, digital twin synchronization, and AI-driven efficiency gains without introducing external risks.

Siemens Defense-in-Depth: Industrial Security

SINEC Secure Connect is designed to operate within Siemens' broader, multi-layered Defense-in-Depth framework. This strategy aligns with IEC 62443 and covers plant security, network security, and system integrity. Plant security establishes physical and administrative protection, while network security combines the Zero Trust overlay of SINEC Secure Connect with SCALANCE industrial firewalls to manage physical cell boundaries. System integrity secures individual automation components, such as SIMATIC controllers, which are built secure by design with cryptographic firmware signing and configuration protections. Together, these layers help ensure that integrating legacy brownfield assets with cloud environments does not compromise operational integrity, while assisting operators in meeting CRA security-by-design mandates and Article 14 rapid reporting requirements.

Recommendations

Based on these trends, ARC recommends that industrial operators take immediate action to secure and digitalize their legacy assets. Operators should begin with comprehensive asset inventories and risk assessments to map active connections and identify unauthorized remote access paths. Traditional network-level VPNs should be phased out in favor of Zero Trust architectures that use micro-segmented, identity-verified overlays to enforce least privilege. All remote connections should implement multi-factor authentication and thorough audit logging to comply with NIS2 requirements.

Given the complexity of OT environments, organizations should partner with specialized OT security providers that understand industrial protocols and can deploy additive solutions without operational downtime. By leveraging non-disruptive, gateway-based overlays, enterprises can securely connect brownfield infrastructure to modern cloud services while safeguarding operational continuity.
 

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