An important principle of defense in depth is that achieving information security requires a balanced focus on the primary elements of people, technology, and operations. People are the users, administrators, managers, and other stakeholders who are involved in the security process. They need to be aware, trained, motivated, and accountable for their security roles and responsibilities. Technology is the hardware, software, network, and other tools that are used to implement the security controls and measures. They need to be selected, configured, updated, and monitored according to the security standards and best practices. Operations are the policies, procedures, processes, and activities that are performed to achieve the security objectives and requirements. They need to be documented, reviewed, audited, and improved continuously to ensure their effectiveness and efficiency.

The other options are not the primary elements of defense in depth, but rather the phases, functions, or outcomes of the security process. Development, testing, and deployment are the phases of the security life cycle, which describes how security is integrated into the system development process. Prevention, detection, and remediation are the functions of the security management, which describes how security is maintained and improved over time. Certification, accreditation, and monitoring are the outcomes of the security evaluation, which describes how security is assessed and verified against the criteria and standards.