Operationalizing Security Principles
Principles as Constraints Security principles should be treated as constraints in Architecture Decision Records (ADRs) and RFCs. Constraints ensure principles are considered. Principles should be encoded as tests and policy-as-code. Encoding enables automated verification. Adherence should be measured with continuous metrics. Metrics show principle compliance. Where principles appear to conflict, make trade-offs explicit, time-bounded, and reviewable. Explicit trade-offs enable informed decisions. Design for Adversarial Conditions Design for failure, not just normal operation. Failure is inevitable. Design for misuse, not just intended use. Attackers misuse functionality. Design for partial compromise, not just full security. Compromise is likely. Assume breach and design for containment. Containment limits damage.Core Security Principles
CIA Triad: Confidentiality, Integrity, Availability
Confidentiality Confidentiality prevents unauthorized disclosure. Data exposure should be minimized. Encryption in transit protects data during transmission. TLS provides confidentiality. Encryption at rest protects stored data. Encryption prevents data theft. Attribute-based access control limits data access. ABAC provides fine-grained control. Privacy constraints protect personal data. Privacy compliance is mandatory. Integrity Integrity prevents unauthorized modification. Data accuracy must be maintained. Strong authentication and authorization verify identity and permissions. AuthN and AuthZ prevent unauthorized changes. Tamper-evident logs detect modifications. Immutable logs provide audit trail. Signed artifacts prove authenticity. Signatures prevent tampering. Immutability controls prevent changes. Immutability ensures integrity. Supply chain provenance verifies origin. Provenance prevents supply chain attacks. Availability Availability ensures service uptime. Systems must be accessible. Capacity planning prevents resource exhaustion. Planning ensures sufficient resources. Graceful degradation maintains partial functionality. Degradation is better than failure. DoS resilience prevents denial of service. Resilience ensures availability. Backpressure prevents overload. Backpressure protects systems. Circuit breakers prevent cascade failures. Circuit breakers isolate failures. Multi-AZ and multi-region deployment provides redundancy. Redundancy ensures availability. Implications Drive threat models that separate impact classes. Separation enables targeted controls. Build compensating controls per impact class. Compensating controls address specific risks. Balance CIA requirements based on data classification. Balance optimizes protection.Defense in Depth
Layered Controls Defense in depth provides overlapping controls at multiple layers. Layers include identity, network, host, application, and data. Identity layer authenticates and authorizes. Identity is first line of defense. Network layer segments and filters traffic. Network controls limit lateral movement. Host layer hardens systems. Host controls prevent compromise. Application layer validates input and output. Application controls prevent exploitation. Data layer encrypts and controls access. Data controls protect information. Assume Single-Control Failure Single controls will fail. Assume failure and plan accordingly. Design escalation paths for control failures. Escalation enables response. Design blast-radius containment. Containment limits damage. Multiple signals improve detection. Multi-signal detection reduces false negatives. Encoding Defense in Depth Layered policies encode defense in depth. Organization SCPs, project IAM, and service policies provide layers. Multi-signal detections combine indicators. Combination improves accuracy. Redundant controls provide backup. Redundancy ensures protection.Least Privilege
Minimize Permissions Minimize permissions by default. Minimal permissions reduce risk. Deny-by-default boundaries require explicit grants. Deny-by-default prevents accidental access. Time-bounded elevation limits privilege duration. Time bounds reduce exposure. Context-bounded elevation limits privilege scope. Context bounds reduce risk. Just-In-Time Access JIT access provides temporary permissions. JIT reduces standing privileges. Short-lived credentials expire automatically. Expiration limits exposure. Scoped tokens limit permissions. Scoping reduces risk. Peer or automated approvals gate access. Approvals ensure appropriate access. Access Broker and Break-glass patterns provide emergency access. Emergency access enables incident response. Periodic Recertification Periodic recertification reviews access. Recertification removes unnecessary access. Evidence-based recertification uses data. Evidence improves accuracy. Automate dormant access revocation. Automation ensures timely revocation. Access should be reviewed quarterly. Regular review prevents privilege creep.Fail Secure and Safe Defaults
Fail Secure On error, degrade to safer state. Safer state reduces risk. Block if policy cannot be evaluated. Blocking prevents unauthorized access. Revoke when signals are stale. Revocation prevents stale permissions. Halt sensitive operations on cryptographic failures. Halting prevents insecure operations. Emit high-signal telemetry on failures. Telemetry enables investigation. Safe Defaults Configuration drift should be non-authoritative. Drift should not grant permissions. Use convergent configuration with GitOps. GitOps ensures known-good state. Failures should revert to known-good configuration. Reversion ensures security. Secure defaults should be provided. Defaults make security easy. Opt-in capabilities require explicit enablement. Opt-in prevents accidental exposure.Separation of Duties
Split Critical Paths Requesters should not be approvers. Separation prevents unilateral action. Approvers should not be deployers. Separation ensures oversight. Deployers should not be requesters. Separation prevents conflicts of interest. Human and machine dual control on production-impacting actions. Dual control prevents mistakes. Prevent Unilateral Risk Changes Policy updates should require code review and security control gates. Review prevents malicious changes. Critical changes should require multiple approvals. Multiple approvals ensure appropriate changes. Separation of duties should be enforced. Enforcement ensures compliance. Encoding Separation of Duties Branch protection prevents direct commits. Protection enforces review. Signed commits prove authorship. Signatures prevent impersonation. Provenance verification validates build process. Verification prevents tampering. Pipeline gates enforce separation. Gates ensure compliance.Additional Modern Principles
Secure by Default Closed surfaces minimize attack surface. Closed surfaces are more secure. Opt-in capabilities require explicit enablement. Opt-in prevents accidental exposure. Hardened baselines provide secure starting point. Baselines reduce configuration errors. Economy of Mechanism Prefer simple, auditable designs. Simplicity reduces bugs. Reduce control overlap that adds complexity without coverage. Overlap creates confusion. Complexity is the enemy of security. Simplicity improves security. Complete Mediation Authorize every access on every request. Authorization prevents unauthorized access. Cache carefully with bounded TTL. Caching can bypass authorization. Revocation should be immediate. Immediate revocation prevents unauthorized access. Open Design Security through transparency and verifiability. Transparency enables review. Avoid secret algorithms. Secret algorithms are unverified. Open design enables peer review. Review improves security. Accountability Immutable, tamper-evident logs provide audit trail. Logs enable investigation. Robust identity enables attribution. Identity shows who did what. Non-repudiation prevents denial. Non-repudiation ensures accountability.Architecture-Level Application
Microservices Architecture Enforce service-to-service authentication with mTLS. mTLS provides mutual authentication. SPIFFE and SPIRE provide workload identity. Workload identity enables service authentication. Scoped tokens limit service permissions. Scoping reduces blast radius. Deny-by-default mesh policies prevent unauthorized communication. Deny-by-default is secure. Service mesh provides policy enforcement. Mesh centralizes security. Data Platforms Tiered data classification drives protection. Classification enables appropriate controls. Data products should have privacy contracts. Contracts define data handling. Row-level and column-level security limit data access. Fine-grained access protects sensitive data. Data lineage tracks data flow. Lineage enables compliance. Usage telemetry monitors data access. Telemetry detects anomalies. ML Systems Protect training data confidentiality. Training data often contains sensitive information. Ensure model integrity through signing. Signing prevents model tampering. Maintain prediction availability. Availability ensures service. Guardrails prevent prompt injection. Prompt injection can compromise models. Guardrails prevent data injection. Data injection can poison models. Multi-Cloud Architecture Control-plane isolation per account and project. Isolation limits blast radius. Platform guardrails as code enforce policies. Guardrails prevent misconfigurations. Control inheritance reduces configuration burden. Inheritance scales security. Boundary tests validate isolation. Tests ensure separation.Decision Framework and Trade-offs
Architecture Decision Records Document decisions as ADRs with explicit principle impacts. ADRs provide rationale. Include alternatives considered. Alternatives show due diligence. Include measurable acceptance criteria. Criteria enable verification. ADRs should be reviewed and approved. Review ensures quality. Risk Burndown Charts Visualize principle adherence over time. Visualization shows progress. Track principle violations. Tracking identifies problems. Set targets for principle compliance. Targets drive improvement. Review progress regularly. Review enables course correction. Principle Violation Management When violating a principle, require compensating control. Compensating control reduces risk. Assign owner for violation. Ownership ensures accountability. Set review date for violation. Review ensures temporary violation. Define removal criteria. Criteria enable resolution. Provide executive visibility. Visibility ensures appropriate risk acceptance.Implementation Tactics
Identity and Access Short-lived credentials reduce exposure. Credentials should expire quickly. Central policy engine (OPA or Cedar) provides consistent authorization. Centralization ensures consistency. Attribute-based and intent-based access provide fine-grained control. Fine-grained control reduces risk. Continuous verification validates access. Verification prevents stale permissions. Secrets Management Brokered access provides secrets without distribution. Brokering reduces exposure. Envelope encryption protects secrets. Encryption provides confidentiality. Hardware-backed roots (HSM, TPM, KMS) protect keys. Hardware provides strong protection. Secrets should be rotated regularly. Rotation limits exposure. Network Security Default-private networks minimize exposure. Private networks are more secure. Egress control prevents data exfiltration. Egress control limits damage. Service segmentation limits lateral movement. Segmentation contains breaches. Authenticated edges verify identity. Authentication prevents unauthorized access. Zero Trust Network Access (ZTNA) eliminates implicit trust. ZTNA improves security. Build and Supply Chain Reproducible builds enable verification. Reproducibility proves integrity. SLSA (Supply-chain Levels for Software Artifacts) provides framework. SLSA improves supply chain security. SBOM (Software Bill of Materials) lists dependencies. SBOM enables vulnerability management. Signed artifacts prove authenticity. Signatures prevent tampering. Provenance checks verify build process. Provenance prevents supply chain attacks. Hermetic builds prevent external influence. Hermetic builds ensure reproducibility. Observability and Monitoring High-fidelity logs provide detailed information. Detail enables investigation. Tamper-evident logs prevent modification. Tamper-evidence ensures integrity. Trace security context through requests. Tracing enables correlation. Golden signals for security controls show control health. Signals enable monitoring.Metrics and Signals
Privilege Creep Metrics Net permissions per user over time measures privilege growth. Growth indicates privilege creep. Percent with admin across environments measures over-privileged users. Admin access should be minimal. Dormant access measures unused permissions. Dormant access should be revoked. Break-Glass Metrics Break-glass frequency measures emergency access usage. Frequency should be low. Break-glass duration measures access time. Duration should be minimal. Justification quality measures appropriateness. Quality ensures legitimate use. Mean Time to Revoke (MTTR) measures revocation speed. MTTR should be minimal. Policy Coverage Metrics Percentage of services behind policy-as-code measures automation. Coverage should be high. Percentage of requests with complete mediation measures authorization coverage. Mediation should be complete. Policy enforcement rate measures compliance. Enforcement should be high. Control Efficacy Metrics Escape rate of findings past SDLC gates measures gate effectiveness. Escape rate should be low. Detection MTTD (Mean Time to Detect) by control layer measures detection speed. MTTD should be minimal. Detection MTTR (Mean Time to Respond) by control layer measures response speed. MTTR should be minimal.Anti-Patterns
Implicit Trust Implicit trust inside perimeters assumes internal safety. Assumption is dangerous. Zero Trust eliminates implicit trust. Zero Trust improves security. All access should be verified. Verification prevents unauthorized access. Shared Long-Lived Credentials Shared credentials prevent attribution. Attribution is essential for accountability. Long-lived credentials increase exposure. Credentials should be short-lived. Individual credentials enable accountability. Individual credentials should be used. Over-Broad Permissions Wildcard permissions grant excessive access. Permissions should be minimal. Least privilege should be enforced. Least privilege reduces risk. Permissions should be scoped. Scoping limits damage. Manual Approvals Without Enforcement Manual approvals without cryptographic enforcement can be bypassed. Enforcement ensures compliance. Cryptographic enforcement prevents bypass. Enforcement should be automated. Policy-as-code provides enforcement. Policy-as-code scales. Unauditable Side Channels Side channels bypass controls. Side channels should be eliminated. All access should be logged. Logging enables audit. Audit trails should be complete. Completeness ensures accountability. Control Sprawl Control sprawl without ownership creates confusion. Ownership ensures accountability. Controls without measurement provide false security. Measurement shows effectiveness. Checkbox security focuses on compliance, not effectiveness. Effectiveness should be measured.Conclusion
Security engineering principles are invariants that guide decisions under ambiguity and pressure. Security engineers operationalize principles into architecture, roadmaps, policies, and SDLC controls. Success requires treating principles as constraints in ADRs, encoding principles as tests and policy-as-code, measuring adherence with continuous metrics, applying principles at architecture level, implementing tactics for identity, secrets, networks, build, and observability, and tracking metrics for privilege, policy coverage, and control efficacy. Organizations that invest in security engineering principles build secure systems that hold up under scale, entropy, and adversarial pressure.References
- NIST SP 800-160 Systems Security Engineering
- NIST SP 800-53 Security and Privacy Controls
- ISO/IEC 27001 Information Security Management
- ISO/IEC 27002 Information Security Controls
- SLSA Supply-chain Levels for Software Artifacts
- CIS Controls v8
- NIST Cybersecurity Framework (CSF) 2.0
- Ross Anderson, Security Engineering (3rd Edition)
- Saltzer and Schroeder, The Protection of Information in Computer Systems