The development phase is the stage of the system development life cycle (SDLC) where the system requirements, design, architecture, and implementation are performed. The development phase is most challenging to implement security controls because it involves complex and dynamic processes that may not be well understood or documented. Security controls are essential for ensuring the confidentiality, integrity, and availability of the system and its data, as well as for complying with regulatory and contractual obligations. However, security controls may also introduce additional costs, risks, and constraints to the development process, such as:

Increased complexity and overhead of testing, verification, validation, and maintenance

Reduced flexibility and agility of changing requirements or design

Increased dependency on external vendors or third parties for security services or products

Increased vulnerability to errors, defects, or vulnerabilities in the code or configuration

Increased difficulty in measuring and reporting on security performance or effectiveness

Therefore, implementing security controls in the development phase requires careful planning, coordination, communication, and collaboration among all stakeholders involved in the SDLC. It also requires a clear understanding of the security objectives, scope, criteria, standards, policies, procedures, roles, responsibilities, and resources for the system. Moreover, it requires a proactive approach to identifying and mitigating potential threats or risks that may affect the security of the system.

Reference= CISM Manual1, Chapter 3: Information Security Program Development (ISPD), Section 3.1: System Development Life Cycle (SDLC)2

1: https://store.isaca.org/s/store#/store/browse/cat/a2D4w00000Ac6NNEAZ/tiles2: https://store.isaca.org/s/store#/store/browse/cat/a2D4w00000Ac6NNEAZ/tiles