Which principle underlies the design of secure IACS systems according to ISA/IEC 62443?

The principle of least privilege is fundamental in the design of secure Industrial Automation and Control Systems (IACS) as outlined in ISA/IEC 62443. This principle asserts that users should be granted the minimum level of access—or privileges—necessary to perform their job functions. By limiting access rights, the potential for unauthorized actions or misuse is significantly reduced. This means that even if a user’s credentials are compromised, the damage that can be inflicted will be limited due to restricted access.

This principle not only helps in protecting sensitive systems from internal threats but also aids in minimizing the attack surface that could be exploited by external adversaries. Implementing the principle of least privilege effectively creates a defense in depth strategy, enhancing the overall security posture of the IACS.

In contrast, while principles such as redundancy and maximum availability pertain to system robustness and uptime, they do not specifically address security concerns in the same proactive manner that the principle of least privilege does. User convenience, while important in user experience, often needs to be carefully balanced with security requirements to prevent oversights that could lead to vulnerabilities. Thus, the principle of least privilege stands out as a critical aspect of designing secure IACS systems according to ISA/IEC 62443.