SA-8(7) — Reduced Complexity

Supplemental Guidance

The principle of reduced complexity states that the system design is as simple and small as possible. A small and simple design is more understandable, more analyzable, and less prone to error. The reduced complexity principle applies to any aspect of a system, but it has particular importance for security due to the various analyses performed to obtain evidence about the emergent security property of the system. For such analyses to be successful, a small and simple design is essential. Application of the principle of reduced complexity contributes to the ability of system developers to understand the correctness and completeness of system security functions. It also facilitates the identification of potential vulnerabilities. The corollary of reduced complexity states that the simplicity of the system is directly related to the number of vulnerabilities it will contain; that is, simpler systems contain fewer vulnerabilities. An benefit of reduced complexity is that it is easier to understand whether the intended security policy has been captured in the system design and that fewer vulnerabilities are likely to be introduced during engineering development. An additional benefit is that any such conclusion about correctness, completeness, and the existence of vulnerabilities can be reached with a higher degree of assurance in contrast to conclusions reached in situations where the system design is inherently more complex. Transitioning from older technologies to newer technologies (e.g., transitioning from IPv4 to IPv6) may require implementing the older and newer technologies simultaneously during the transition period. This may result in a temporary increase in system complexity during the transition.