Phase 3: Trust Boundary Evaluation

Phase 3: Trust Boundary Evaluation

Type: Evaluative Executor: LLM Knowledge: Security Principles (ZT, SOD, LP), security-design.yaml

⚠️ MANDATORY OUTPUT RULES

CRITICAL: Phase 3 requires TWO outputs - a YAML data file AND a Markdown report.

Dual Output Requirement

┌─────────────────────────────────────────────────────────────────────┐
│  PHASE 3 MUST PRODUCE TWO FILES:                                    │
├─────────────────────────────────────────────────────────────────────┤
│                                                                      │
│  1. DATA FILE (PRIMARY - Write First!)                              │
│     Path: .phase_working/{SESSION_ID}/data/P3_boundary_context.yaml │
│     Purpose: Structured data for P4 to read                         │
│     Format: Valid YAML with schema_version: "3.0.0 (20260201a)"                   │
│                                                                      │
│  2. REPORT FILE (SECONDARY - Write After Data!)                     │
│     Path: .phase_working/{SESSION_ID}/reports/P3-TRUST-BOUNDARY.md  │
│     Purpose: Human-readable trust boundary analysis                 │
│     Format: Markdown with diagrams and matrices                     │
│                                                                      │
│  INPUT REQUIREMENT:                                                  │
│     Read: .phase_working/{SESSION_ID}/data/P2_dfd_elements.yaml     │
│     ❌ DO NOT read P2's .md report for data extraction              │
│     ✅ REQUIRED: Parse P2's YAML for dfd_elements                   │
│                                                                      │
└─────────────────────────────────────────────────────────────────────┘

Required Data Sections in YAML

Validation Gate

Phase 3 CANNOT complete until:

1. .phase_working/{SESSION_ID}/data/P3_boundary_context.yaml exists and is valid YAML
2. Every DFD element mapped to a trust boundary zone
3. All cross-boundary flows have security controls documented
4. .phase_working/{SESSION_ID}/reports/P3-TRUST-BOUNDARY.md exists

Input Context

← P2: dfd_elements from .phase_working/{SESSION_ID}/data/P2_dfd_elements.yaml

⚠️ MANDATORY: Query P2 Data Before Analysis

Before starting P3 analysis, LLM MUST execute these queries to obtain P2 data:

# Step 1: Get P2 summary for DFD overview
python scripts/phase_data.py --query --phase 2 --summary --root {PROJECT_ROOT}

# Step 2: Get detailed DFD elements (REQUIRED for boundary mapping)
python scripts/phase_data.py --query --phase 2 --type dfd --root {PROJECT_ROOT}

# Step 3: Get data flows (REQUIRED for cross-boundary analysis)
python scripts/phase_data.py --query --phase 2 --type flows --root {PROJECT_ROOT}

Or read YAML directly:

# PRIMARY source - REQUIRED
cat .phase_working/{SESSION_ID}/data/P2_dfd_elements.yaml

CRITICAL: Do NOT generate P3 trust boundaries from memory. MUST read P2 DFD data first!

Output Context

→ P4: boundary_context {boundaries[], interfaces[], data_nodes[], cross_boundary_flows[]}

Core Analysis Goal

Based on DFD, identify trust boundaries, key interfaces, and data nodes; evaluate security posture at boundary crossings.

Knowledge Reference

Security Principles:

• Zero Trust (ZT): Never trust, always verify
• Separation of Duties (SOD): Critical ops require multiple parties
• Least Privilege (LP): Minimum permissions required
• Least Agency (LA): Limit AI agent autonomy

Security Domains: AUTHN, AUTHZ, API from security-design.yaml

Error Handling

Fallback Strategy: If boundary analysis cannot complete due to data gaps, document known boundaries and mark incomplete zones with status: partial and gaps: ["description"].

Trust Boundary Types

Analysis Tasks

1. Identify Trust Boundaries

For each boundary:

• Assign ID: TB-xxx
• Determine type (Network/Process/User/Data/Service)
• Define scope (which elements are inside)
• Identify crossing points

2. Analyze Cross-Boundary Flows

For each data flow crossing a boundary:

• Source boundary zone
• Destination boundary zone
• Security controls at crossing
• Risk assessment

3. Evaluate Interface Security

For each cross-boundary interface:

• Authentication mechanism
• Authorization checks
• Data validation
• Encryption status

4. Map Sensitive Data Nodes

Identify where sensitive data resides relative to boundaries:

• Which boundary zone
• Access controls
• Encryption status

Output Structure

boundary_context:
  boundaries:
    - id: TB-001
      name: "Internet Boundary"
      type: Network
      description: "Boundary between internet and DMZ"
      inside: [P-001]           # Elements inside
      outside: [EI-001, EI-002] # Elements outside
      crossing_points:
        - flow_id: DF-001
          direction: inbound
          controls: [TLS, WAF, Rate-Limit]

  interfaces:
    - id: IF-001
      boundary: TB-001
      entry_side: "Internet"
      exit_side: "DMZ"
      protocol: HTTPS
      authentication: "None (public endpoint)"
      authorization: "N/A"
      validation: "Input sanitization"
      encryption: "TLS 1.3"
      risk_level: HIGH

  data_nodes:
    - id: DN-001
      data_store: DS-001
      data_types: ["User PII", "Credentials"]
      sensitivity: CRITICAL
      boundary_zone: "Internal Network"
      access_controls: ["Role-based", "MFA required"]
      encryption:
        at_rest: true
        in_transit: true

  cross_boundary_flows:
    - flow_id: DF-001
      source_zone: "Internet"
      dest_zone: "DMZ"
      boundaries_crossed: [TB-001]
      data_sensitivity: MEDIUM
      security_controls:
        authentication: "Session token"
        encryption: "TLS 1.3"
        validation: "Input sanitization"
      risk_assessment:
        level: MEDIUM
        concerns: ["Public exposure", "Credential handling"]

Boundary Diagram Template

┌─────────────────────────────────────────────────────────────────┐
│                     Trust Boundary Diagram                       │
├─────────────────────────────────────────────────────────────────┤
│                                                                  │
│  ╔══════════════════════════════════════════════════════════╗   │
│  ║ TB-001: Internet Boundary                                 ║   │
│  ╠══════════════════════════════════════════════════════════╣   │
│  ║                                                           ║   │
│  ║  ┌─────────┐                                             ║   │
│  ║  │ EI-001  │                                             ║   │
│  ║  │Web User │──────────┐                                  ║   │
│  ║  └─────────┘          │ DF-001                           ║   │
│  ║                       │ [TLS, WAF]                       ║   │
│  ╚═══════════════════════╪══════════════════════════════════╝   │
│                          │                                       │
│  ╔═══════════════════════╪══════════════════════════════════╗   │
│  ║ TB-002: DMZ          ▼                                    ║   │
│  ╠══════════════════════════════════════════════════════════╣   │
│  ║  ┌─────────┐        ┌─────────┐                          ║   │
│  ║  │  P-001  │───────▶│  P-002  │                          ║   │
│  ║  │API Gate │ DF-002 │Auth Svc │                          ║   │
│  ║  └─────────┘        └────┬────┘                          ║   │
│  ╚═══════════════════════════╪══════════════════════════════╝   │
│                              │                                   │
│  ╔═══════════════════════════╪══════════════════════════════╗   │
│  ║ TB-003: Internal Network  │ DF-003                        ║   │
│  ╠═══════════════════════════╪══════════════════════════════╣   │
│  ║                           ▼                               ║   │
│  ║                     ┌─────────┐                           ║   │
│  ║                     │ DS-001  │                           ║   │
│  ║                     │User DB  │                           ║   │
│  ║                     └─────────┘                           ║   │
│  ╚══════════════════════════════════════════════════════════╝   │
│                                                                  │
└─────────────────────────────────────────────────────────────────┘

Security Assessment Matrix

Boundary Issues to Identify

1. Missing Controls: Boundaries without adequate authentication
2. Weak Encryption: Unencrypted or weak encryption at crossings
3. Excessive Permissions: Cross-boundary access with excessive privileges
4. Missing Validation: Input not validated at boundary crossings
5. Sensitive Data Exposure: Sensitive data crossing to lower-trust zones

Report Template

# P3: Trust Boundary Evaluation

## Boundary Summary

| Boundary | Type | Elements Inside | Crossing Flows |
|----------|------|-----------------|----------------|
| TB-001 | Network | P-001 | DF-001 |
| TB-002 | Network | P-001, P-002 | DF-002, DF-003 |

## Trust Boundary Diagram

[ASCII diagram]

## Cross-Boundary Flow Analysis

### DF-001: User Request (Internet → DMZ)
- **Source Zone**: Internet
- **Dest Zone**: DMZ
- **Security Controls**: TLS 1.3, WAF, Rate Limiting
- **Risk Level**: Medium
- **Concerns**: Public exposure

## Interface Security Assessment

[Assessment matrix]

## Sensitive Data Mapping

| Data Node | Location | Sensitivity | Protection |
|-----------|----------|-------------|------------|
| DN-001 | Internal | CRITICAL | Encrypted, RBAC |

## Boundary Findings

[yaml:boundary_findings block - see below]

```yaml:boundary_findings
findings:
  - id: F-P3-001
    type: boundary
    title: "Finding title"
    description: "Detailed description"
    severity: HIGH      # CRITICAL|HIGH|MEDIUM|LOW|INFO
    category: missing_control|weak_encryption|excessive_permission|unprotected_crossing
    location:
      boundary_id: TB-xxx
      interface_id: IF-xxx
      flow_id: DF-xxx
    affected_elements:
      - type: trust_boundary
        id: TB-xxx
      - type: cross_boundary_flow
        id: DF-xxx
    security_relevance: "Why this matters for security"
    crossing_risk: HIGH  # Risk level of boundary crossing
    recommended_action: "What to investigate in later phases"

summary:
  total: 0
  by_severity:
    critical: 0
    high: 0
    medium: 0
    low: 0
    info: 0
  by_category:
    missing_control: 0
    weak_encryption: 0
    excessive_permission: 0
    unprotected_crossing: 0

Finding Categories:

• missing_control: Boundary crossing without security control
• weak_encryption: Inadequate encryption at boundary
• excessive_permission: Cross-boundary access with excessive privileges
• unprotected_crossing: Input not validated at boundary

Recommendations

1. ...
2. ...

---

## Completion Checklist

Before marking Phase 3 complete:

- [ ] All trust boundaries identified (TB-xxx)
- [ ] All cross-boundary flows analyzed
- [ ] Interface security assessed
- [ ] Sensitive data nodes mapped
- [ ] Trust boundary diagram included
- [ ] yaml:boundary_findings present (even if empty)
- [ ] Boundary issues documented
- [ ] Validation passed

---

**End of Phase 3 Instructions** (~200 lines, ~1.5K tokens)