Module 16 of 20 — Advanced Domains

Security Architecture & Design Principles

Security architecture translates principles into technical implementations. Well-designed systems are resilient by default, with clear trust boundaries and failure modes. This module covers architectural patterns, threat modeling, and design principles for secure systems.

Fundamental Security Principles

These principles guide secure architecture design. They are timeless guidelines rather than specific technologies.

Zero Trust

Never trust, always verify. Authenticate and authorize every request.

Example: Google BeyondCorp model—employees access internal apps from any network with device trust scoring.
How: Micro-segmentation, identity-aware proxy, continuous validation.

Defense in Depth

Multiple overlapping controls so single failure doesn't compromise security.

Example: Firewall + IDS + EDR + SIEM + Security Awareness all protecting the same asset.
How: Layered architecture, redundant controls, fail-closed design.

Fail-Secure

Systems default to secure state when failure occurs.

Example: Door locks engage on power loss rather than unlock.
How: Fail-safe defaults in configuration, automatic lockdown on error.

Least Privilege

Grant minimum permissions necessary for function.

Example: AWS IAM policies scoped to specific resources and actions.
How: Role-based access, just-in-time access, regular permission reviews.

Secure by Design

Security built into architecture from inception, not added later.

Example: Threat modeling during design phase, security requirements in user stories.
How: Security architects in design reviews, threat modeling, security testing.

Security Architecture Patterns

Patterns provide proven structures for common security requirements.

Demilitarized Zone (DMZ)

Purpose: Isolate external-facing services from internal network.
Components: Web server, application server, reverse proxy, jump host.
Risks: Lateral movement if compromised, insider threat from zone.

Air Gap

Purpose: Physically isolate critical systems from other networks.
Components: Dedicated hardware, data diodes, removable media procedures.
Risks: Human error during data transfer, supply chain for removable media.

Microsegmentation

Purpose: Fine-grained network isolation using software-defined perimeters.
Components: Software firewalls, service mesh, identity-aware proxies.
Risks: Policy complexity, east-west traffic visibility gaps.

Security Orchestration

Purpose: Automate security responses across multiple tools.
Components: SOAR platform, playbooks, integrated security tools.
Risks: False positives triggering disruptive actions, tool dependency.

Threat Modeling Methods

Threat modeling identifies potential attacks before implementation. Choose methods based on audience and design stage.

STRIDE

Categorizes threats: Spoofing, Tampering, Repudiation, Information disclosure, Denial of service, Elevation of privilege.

Steps: Identify assets, trust boundaries, data flows, then apply STRIDE to each flow.

Tools: Microsoft Threat Modeling Tool, OWASP Threat Dragon.

PASTA

Seven-step process linking business objectives to attacker techniques.

Steps: Define objectives, technical scope, application decomposition, threat analysis, attack modeling, risk analysis, countermeasure definition.

Tools: RiskWatch, threat modeling spreadsheets.

OCTAVE

Operationally Critical Threat, Asset, and Vulnerability Evaluation focuses on organization risk.

Steps: Build risk-based security strategy, identify assets and vulnerabilities, analyze risks, develop mitigation plan.

Tools: OCTAVE Allegro, self-assessment worksheets.

Security Metrics & KPIs

Measuring security effectiveness requires metrics tied to business outcomes.

Detection Metrics

  • Mean Time to Detect (MTTD) - Target: < 24 hours
  • Detection accuracy - True positive rate vs false positive rate
  • Coverage percentage - Assets monitored vs total assets

Response Metrics

  • Mean Time to Respond (MTTR) - Target: < 1 hour for critical
  • Automation rate - Percentage of alerts handled automatically
  • Containment effectiveness - Lateral movement prevented

Prevention Metrics

  • Patch compliance - Percentage of systems up to date
  • Security test pass rate - Applications passing security gates
  • Training completion - Staff completing security awareness

Key Takeaways

  • Zero Trust and Defense in Depth are foundational architectural principles.
  • Threat modeling during design prevents expensive rework later.
  • Architecture patterns provide proven structures for common requirements.
  • Metrics drive improvement—track MTTD, MTTR, and prevention rates.
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