Towards AI-Guided Security Hardening of Industrial Systems Based on IEC 62443
: Industrial systems are increasingly exposed to cyber threats, requiring stronger design methodologies to ensure resilience and security. In critical infrastructures, compliance with standards such as IEC 62443 is essential for ensuring security throughout the system lifecycle. This paper investigates a secure-by-design engineering process focusing on the initial architectural design and examines the role that AI-powered agents can play in supporting it, as well as the conditions required for their effective and reliable use. This study experiments with an open-source agentic framework to generate zone-and-conduit architectures from an initial system blueprint. A multi-agent workflow is implemented, including agents responsible for architecture generation, compliance verification against IEC 62443 requirements, and security stress testing using attack tree analysis. A drinking water utility case study, subject to NIS regulatory constraints, is used to compare AI-assisted and manually produced architectures. The results highlight both the benefits and limitations of AI-assisted design, leading to the identification of recommendations and open issues for further research, with potential applicability beyond the industrial domain.