Which of the following is NOT a key principle of secure software design?

The principle that is NOT a key aspect of secure software design is open access. In the context of secure software development, the idea of open access typically implies that users have unrestricted entry to systems or data, which fundamentally undermines security. Secure software design emphasizes protecting sensitive information and functionalities, making it crucial to restrict access based on the principles of least privilege, defense in depth, and fail securely.

Least privilege ensures that users and systems operate using the minimum amount of privilege necessary to perform their tasks, which helps to reduce the attack surface. Defense in depth involves implementing multiple layers of security controls so that if one layer fails, others will still provide protection. Fail securely emphasizes that if a system does encounter an error or failure, it should do so in a way that does not compromise security, ensuring that any failure will not expose sensitive data or grant unauthorized access.

Each of these principles is fundamental to creating a robust security posture in software design, while open access contrasts with these principles by advocating for less restrictive measures that could lead to vulnerabilities.