Security Aspects of Zones and Conduits in IEC 62443

The IEC 62443 standard defines that, based on risk assessment, different parts of an Industrial Automation and Control System (IACS) may have different security levels, and that parts with the same security level can be designated as separate zones. Furthermore, communication between different zones, both intra-IACS and inter-IACS, can be done via conduits. In this article, we argue that zones and particularly conduits can benefit from more detailed discussions of their architecture and implementation. Consequently, as novel contributions we (1) describe detailed principles for implementing conduits; (2) outline a process for connecting zones with potentially different Security Levels (SLs), expressed in the form of a flow chart; and (3) discuss challenges related to the application of zones and conduits in practice.