Embedded Linux systems in security-critical environments shall comply with rigorous standards such as IEC 62443-4-2 or satisfy comprehensive risk assessment requirements. But how to apply security standards or risk assessments to a real world linux system? This presentation introduces a systematic methodology for translating high-level security requirements into a practical, implementable architecture for embedded Linux systems.

Our approach integrates security requirements throughout the architecture design phase by assigning each to specific lifecycle phases and corresponding software components. These requirements are progressively refined and accumulated alongside functional specifications, guiding the selection of optimal open-source software components. For instance, this process may determine the use of lighttpd with HTTPS or nginx as a reverse proxy to fulfill specific security objectives. Furthermore the requirements are addressed through build-time or runtime configuration, with only rare cases necessitating code modifications.

The resulting design achieves a level of detail that enables efficient implementation in any Linux build system while supporting comprehensive testing and verification. Traceability mechanisms can be used to demonstrate that all initial requirements are satisfied through testing, ensuring compliance with the applied standard. When based on a risk assessment, these traces verify that all defined mitigation are implemented, confirming the complete deployment of security measures.

This methodology yields lean software systems with a minimal package footprint, that can be implemented strait-forward with in budget as late readjustments due not unmet security requirements are avoided.

Furthermore this methodology significantly improves post-deployment security maintenance by reducing the attack surface and the number of applicable CVEs. Furthermore, the approach allows to systematically incorporate defense-in-depth principles, ensuring device security even when individual vulnerabilities compromise the first line of defense.

Short Bio:

Thomas Brinker is a Senior System Engineer and Project Manager at emlix GmbH. He specializes in the architecture and design of embedded Linux-based systems for medical technology, consumer electronics, and industrial applications, as well as their network integration.