The main principle of __________ is to build layers of redundant and complementary security tools, policies, controls, and practices around the organization’s information and assets.

Defense in Depth also known as DiD, is referred to as an approach to the cyber-security under which array of defensive techniques are layered so as to protect the valuable information and data. If one of these mechanism tends to fail, another one will step up immediately in order to thwart the attack. This approach that has intentional redundancies tends to increases security and protection of a system. It is also referred to as "castle approach" since it also executes the same layered defense mechanism of the medieval castle.