Requirements engineering is the disciplined process of defining what a system must do, checking that those needs are correct, and managing changes as the project evolves. It turns vague business goals into testable, traceable requirements, such as who can access data, how authentication should work, what gets logged, and which events must trigger alerts.
In cyber security, strong requirements engineering is a control in itself. Many security failures start as missing, unclear, or conflicting requirements: a feature ships without multi-factor authentication, logs are not retained long enough for investigation, or access rules are left open to interpretation. Attackers often benefit from these gaps, while defenders use requirements to build secure defaults, define acceptance tests, and prove that critical controls were implemented. Good requirements engineering also helps teams manage change safely when new risks, regulations, or integrations appear.