The DRY principle means “Don’t Repeat Yourself.” It is a design rule that says a piece of knowledge, such as a business rule, validation check, or security setting, should exist in one clear place instead of being copied across a codebase. In cyber security, DRY matters because duplicated logic can drift out of sync: one copy gets updated, another is forgotten, and the system ends up enforcing different rules in different places.
That drift creates risk in authentication, authorization, patching, encryption settings, and configuration management. Attackers often benefit from these inconsistencies, because one outdated copy of a rule or control can leave a weaker path open. Defenders use DRY to centralize sensitive logic, reduce maintenance errors, and make verification easier. If a security rule changes once, it is far easier to test and trust than when it is repeated in many locations.