Using DFDs in the Threat Modeling Process

DFDs drive systematic threat identification by providing structure for analysis. For each data flow crossing a trust boundary, consider STRIDE threats. Can the flow be intercepted (information disclosure)? Can it be modified (tampering)? Can the source be spoofed? This systematic approach ensures comprehensive threat coverage.

Use DFDs to guide security testing by identifying what needs testing and how. Each trust boundary suggests authorization tests. Each data flow indicates injection points for fuzzing. Each data store requires access control verification. Test cases derived from DFDs provide better coverage than ad-hoc testing approaches.

DFDs facilitate security discussions by providing a common visual reference. Developers, architects, security professionals, and even non-technical stakeholders can understand and contribute when discussions center on clear diagrams. Mark up DFDs during threat modeling sessions to capture insights and decisions. These marked diagrams become valuable documentation of security analysis.

Maintain DFDs as living documents that evolve with your system. Version control DFD source files alongside code. Update diagrams when architecture changes. Review DFDs during security assessments to ensure they remain accurate. Outdated DFDs provide false security and might miss new threat vectors introduced by system evolution.