SA-17(5)—Conceptually Simple Design

The principle of reduced complexity states that the system design is as simple and small as possible (see SA-08(07)). A small and simple design is easier to understand and analyze and is also less prone to error (see AC-25, SA-08(13)). The principle of reduced complexity 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 and 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 important benefit of reduced complexity is that it is easier to understand whether the 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 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.