At which phase of the SDLC process should security begin participating?

Integrating security practices into the SDLC as early as the requirements gathering phase allows for security considerations to be built in from the ground up, identifying potential security risks and defining necessary controls before significant development effort is invested. This "shift-left" approach is crucial for developing secure software efficiently and cost-effectively, as fixing security flaws later is more expensive.

While requirements analysis is early, security involvement should precede it to influence the initial capture of security-related requirements.

Engaging security only at the design phase means that fundamental security requirements might have been missed or are difficult to incorporate without re-scoping.

Waiting until the testing phase to involve security is too late, as vulnerabilities discovered at this stage are much more costly and time-consuming to remediate.