# Technical Handover Document - LLM Security Firewall

**Date:** 2025-12-01
**Version:** 5.0.0rc1
**Status:** Release Candidate
**Document Type:** Technical Handover

---

## Executive Summary

This document provides a technical handover for the LLM Security Firewall project. The system implements a bidirectional security framework for human/LLM interfaces using a hexagonal architecture pattern. Current status: release candidate with critical security fixes implemented, but significant gaps remain in adversarial bypass coverage and operational readiness.

**Key Metrics:**
- Adversarial bypasses fixed: 2/34 (high+critical severity)
- Test coverage: Claims 95%, actual coverage unverified
- P99 latency: <200ms (maintained)
- Memory usage: 1355MB in batch processing (exceeds 300MB limit by 4.5x)
- False positive rate: <25% (improved from 40%, target: <5%)

---

## System Architecture

### Core Components

**Firewall Engine** (`src/llm_firewall/core/firewall_engine_v2.py`)
- Main decision engine
- Risk score aggregation
- Policy application
- Unicode security analysis

**Normalization Layer** (`src/hak_gal/layers/inbound/normalization_layer.py`)
- Recursive URL/percent decoding
- Unicode normalization (NFKC)
- Zero-width character removal
- Directional override character removal

**Pattern Matching** (`src/llm_firewall/rules/patterns.py`)
- Regex-based pattern detection
- Concatenation-aware matching
- Evasion pattern detection

**Cache System** (`src/llm_firewall/cache/decision_cache.py`)
- Exact match caching (Redis)
- Semantic caching (LangCache)
- Hybrid mode support
- Circuit breaker pattern (AdapterHealth)
- Fail-open behavior (security concern)

**Adapter Health** (`src/llm_firewall/core/adapter_health.py`)
- Circuit breaker implementation
- Health metrics tracking
- Failure threshold management
- Recovery timeout handling

### Architecture Pattern

The system follows a hexagonal architecture with functional adapters and constructor injection. Core business logic is separated from infrastructure concerns, though strict port/adapter separation is not fully enforced (architectural debt documented).

---

## Implemented Security Fixes

### 1. Zero-Width Unicode Bypass (adv_001)

**Status:** Fixed

**Implementation:**
- Added `_remove_stealth_chars()` method in `normalization_layer.py`
- Enhanced Unicode sanitizer to detect zero-width characters
- Risk score increased by 0.6 when zero-width characters detected
- Normalization removes zero-width characters before pattern matching

**Files Modified:**
- `src/hak_gal/layers/inbound/normalization_layer.py`
- `src/hak_gal/layers/inbound/sanitizer.py`
- `src/llm_firewall/core/firewall_engine_v2.py`

**Test Status:** PASSED (`tests/security/test_implemented_fixes.py::test_zero_width_bypass_fixed`)

---

### 2. RLO/Bidi Bypass (adv_002)

**Status:** Fixed

**Implementation:**
- Correct flag mapping in Unicode sanitizer (`has_bidi`, `has_directional_override`)
- Risk score increased by 0.5 when RLO/Bidi characters detected
- Bidi controls removed from sanitized text but flagged in metadata

**Files Modified:**
- `src/hak_gal/layers/inbound/sanitizer.py`
- `src/llm_firewall/core/firewall_engine_v2.py`

**Test Status:** PASSED (`tests/security/test_implemented_fixes.py::test_rlo_bypass_fixed`)

---

### 3. Concatenation Bypass

**Status:** Fixed

**Implementation:**
- Implemented concatenation-aware pattern matching
- Functions: `detect_concatenated_pattern()`, `build_concatenation_aware_regex()`
- Risk score increased by 0.5 when concatenated patterns detected
- Integrated into RobustPatternMatcher

**Files Modified:**
- `src/llm_firewall/rules/patterns.py`
- `src/llm_firewall/core/firewall_engine_v2.py`

**Test Status:** PASSED (`tests/security/test_implemented_fixes.py::test_concatenation_bypass_fixed`)

---

### 4. Kids Policy False Positives

**Status:** Improved (not fully resolved)

**Implementation:**
- Increased cumulative risk threshold from 0.65 to 0.8
- Improved risk score calculation
- Enhanced Unicode flag handling

**Files Modified:**
- `kids_policy/firewall_engine_v2.py` (line 165)

**Test Status:** PASSED with limitations (`tests/security/test_implemented_fixes.py::test_kids_policy_false_positives_improved`)
- Current rate: <25% (target: <5%)
- Remaining issue: Some legitimate educational queries still blocked

---

## Critical Issues Remaining

### P0 - Security Critical

**1. Adversarial Bypass Coverage Gap**
- Status: 32/34 high+critical severity vectors unaddressed
- Evidence: `data/gpt5_adversarial_suite.jsonl` contains 50 vectors
  - Critical: 10 vectors
  - High: 24 vectors
  - Fixed: 2 vectors (adv_001, adv_002)
- Risk: Unknown attack surface, system may be vulnerable to documented bypass techniques
- Reference: `docs/CRITICAL_ISSUES_REGISTER.md`

**2. Fail-Open Behavior on Cache Failure**
- Status: Security violation
- Evidence: `decision_cache.py` returns `None` on Redis errors (14 instances)
- Problem: Cache failure should trigger fail-safe (block), not fail-open (allow)
- Risk: Attacker could disable Redis to bypass caching layer
- Location: `src/llm_firewall/cache/decision_cache.py`

**3. WASM Sandbox Timeout Not Enforced**
- Status: Not found (may not be implemented)
- Problem: No hardware interrupt or signal-based timeout enforcement
- Risk: DoS vulnerability through infinite loops
- Action Required: Verify existence, implement timeout if present

### P1 - Performance & Memory

**4. Batch Processing Memory Leak**
- Status: Exceeds limit by 4.5x
- Current: 1355.7MB (limit: 300MB)
- Root causes: Unbounded embedding cache, session state accumulation
- Action Required: Streaming batch processing, LRU eviction, checkpointing

**5. Embedding Cache Unbounded Growth**
- Status: No size limits, TTL, or eviction policy
- Problem: Cache grows until memory exhaustion
- Action Required: MAX_SIZE limit, TTL support, LRU eviction

**6. Streaming Buffer Not Implemented**
- Status: 32 MiB limit mentioned in design but not implemented
- Action Required: Verify requirement, implement if needed

### P2 - Integration & Operations

**7. Redis Cloud Tests Skipped**
- Status: 0% test coverage for Redis Cloud integration
- Problem: Tests skipped due to missing ENV vars
- Action Required: Add credentials to CI, implement mocks/fixtures

**8. Shadow-Allow Mechanism Undocumented**
- Status: Functionality exists but not documented or monitored
- Problem: No visibility into shadow-allow decisions
- Action Required: Document mechanism, add monitoring metrics

**9. Configuration in Environment Variables (Unencrypted)**
- Status: API keys and passwords stored in plaintext
- Problem: No KMS integration, no encrypted config files
- Action Required: Plan KMS integration, implement encrypted config

---

## Test Results

### Security Fix Tests

All tests in `tests/security/test_implemented_fixes.py`:
- `test_zero_width_bypass_fixed`: PASSED
- `test_rlo_bypass_fixed`: PASSED
- `test_concatenation_bypass_fixed`: PASSED
- `test_kids_policy_false_positives_improved`: PASSED (with limitations)

### Integration Tests

- `test_circuit_breaker_implementation`: PASSED
- `test_p99_latency_adversarial_inputs`: PASSED
- `test_cache_mode_switching`: PASSED
- `test_false_positive_tracking`: IMPROVED (40% → <25%)
- `test_memory_usage_under_300mb`: FAILED (1355.7MB measured)

### Adversarial Test Suite

- Total vectors: 50
- Critical severity: 10
- High severity: 24
- Fixed: 2 (adv_001, adv_002)
- Remaining: 32 high+critical vectors untested/unfixed

### Test Coverage

- Claimed: 95% domain layer
- Actual: Unverified (Redis tests skipped, WASM tests mock-only)
- Estimated: <70% actual coverage

---

## Performance Characteristics

### Latency

- P99 latency: <200ms for standard inputs (maintained)
- Adversarial inputs: <200ms (requirement met)
- Cache hit latency: <100ms (Redis Cloud), <1ms (local Redis)

### Memory

- Single request: <50MB (acceptable)
- Batch processing: 1355.7MB (exceeds 300MB limit by 4.5x)
- Root causes: Unbounded embedding cache, session state accumulation

### Throughput

- No degradation observed after security fixes
- Cache hit rate: 30-50% (exact), 70-90% (hybrid)

---

## Dependencies

**Core:**
- numpy>=1.24.0
- scipy>=1.11.0
- scikit-learn>=1.3.0
- pyyaml>=6.0
- blake3>=0.3.0
- requests>=2.31.0
- psycopg[binary]>=3.1.0
- redis>=5.0.0
- pydantic>=2.0.0
- psutil>=5.9.0
- cryptography>=41.0.0

**Machine Learning:**
- sentence-transformers>=2.2.0
- torch>=2.0.0
- transformers>=4.30.0
- onnx>=1.14.0
- onnxruntime>=1.16.0

---

## Configuration

### Cache Modes

Configure via `CACHE_MODE` environment variable:
- `exact` (default): Redis exact match cache
- `semantic`: LangCache semantic search
- `hybrid`: Both caches in sequence

### Redis Configuration

```bash
export REDIS_URL=redis://:password@host:6379/0
export REDIS_TTL=3600  # Optional: Cache TTL in seconds
```

For Redis Cloud:
```bash
export REDIS_CLOUD_HOST=host
export REDIS_CLOUD_PORT=port
export REDIS_CLOUD_USERNAME=username
export REDIS_CLOUD_PASSWORD=password
```

### Kids Policy Threshold

Location: `kids_policy/firewall_engine_v2.py` line 165
```python
CUMULATIVE_RISK_THRESHOLD = 0.8  # Increased from 0.65
```

### Risk Score Weights

Location: `src/llm_firewall/core/firewall_engine_v2.py`
- Zero-width detection: +0.6
- RLO/Bidi detection: +0.5
- Concatenation detection: +0.5
- Encoding anomalies: +0.3 * anomaly_score
- Block threshold: >= 0.7

---

## Known Limitations

### 1. Adversarial Bypass Coverage

- 32/34 high+critical severity vectors unaddressed
- Unknown which vectors bypass the system
- No systematic testing of all 50 vectors
- Recommendation: Run full adversarial suite, document bypasses, prioritize fixes

### 2. Fail-Open Security Violation

- Cache failures result in fail-open (allow) behavior
- Should be fail-safe (block) with manual override
- Recommendation: Implement fail-safe, add override mechanism, add monitoring

### 3. Memory Usage

- Batch processing exceeds 300MB limit by 4.5x
- Embedding cache unbounded
- Recommendation: Implement LRU cache, streaming processing, checkpointing

### 4. Test Coverage

- Claims unverified
- Redis tests skipped
- WASM tests mock-only
- Recommendation: Measure actual coverage, fix skipped tests, set realistic targets

### 5. CI/CD Gates

- Gates exist only in documentation
- No enforcement in CI pipeline
- Recommendation: Implement adversarial resilience gate, memory limit checks, block on failures

---

## Roadmap

See `ROADMAP.md` for detailed 4-phase plan:

**Phase 1: Stabilization & Security Hardening** (6-8 weeks)
- Fix 32/34 remaining high+critical bypasses
- Implement fail-safe behavior
- Resolve memory issues
- Target: v3.0.0 release

**Phase 2: Extension & Benchmarking** (3-4 months)
- OWASP LLM Top 10 coverage (90%)
- External benchmark validation
- RAG pipeline security
- Target: v4.0.0 release

**Phase 3: Usability & Adoption** (6 months)
- Developer experience improvements
- PyPI package
- Documentation
- Target: 1000+ stars, 50+ contributors

**Phase 4: Enterprise & Market Leadership** (12+ months)
- Enterprise features
- Formal verification
- Market positioning
- Target: Fortune 500 customer

---

## Immediate Action Items (Next 30 Days)

### Priority 1: CI/CD Enforcement

1. Create `run_all_tests.sh` script testing all 50 adversarial vectors
2. Fail build on any bypass detection
3. Activate performance gates:
   - P99 latency <200ms
   - Memory <300MB
   - Test coverage >95%
4. Block merges on gate failures

### Priority 2: Architecture Cleanup

1. Remove Redis/external adapter dependencies from domain layer
2. Implement proper interfaces (Protocols) for adapters
3. Implement monitoring wrapper with promised metrics
4. Document monitoring setup

### Priority 3: External Validation

1. Run against `garak` benchmark suite
2. Document results (even if imperfect)
3. Publish results in README
4. Identify gaps and prioritize fixes

---

## Testing Instructions

### Run Security Fix Tests

```bash
pytest tests/security/test_implemented_fixes.py -v
```

### Run Integration Tests

```bash
pytest tests/integration/test_external_review_validation.py -v
```

### Run Adversarial Bypass Analysis

```bash
pytest tests/security/test_adversarial_bypass_fix.py::TestAdversarialBypassFix::test_identify_bypasses -v
```

### Run All P0 Tests

```bash
pytest tests/integration/test_external_review_validation.py tests/unit/test_circuit_breaker.py tests/unit/test_adapter_health.py -v
```

### Run Full Adversarial Suite

```bash
# TODO: Create run_all_tests.sh script
python -m pytest tests/security/test_adversarial_bypass_fix.py -v
```

---

## File Structure

### Core Security Files

- `src/llm_firewall/core/firewall_engine_v2.py` - Main firewall engine
- `src/hak_gal/layers/inbound/normalization_layer.py` - Input normalization
- `src/hak_gal/layers/inbound/sanitizer.py` - Unicode sanitization
- `src/llm_firewall/rules/patterns.py` - Pattern matching
- `src/llm_firewall/cache/decision_cache.py` - Decision caching
- `src/llm_firewall/core/adapter_health.py` - Circuit breaker
- `kids_policy/firewall_engine_v2.py` - Kids Policy engine

### Test Files

- `tests/security/test_implemented_fixes.py` - Security fix tests
- `tests/security/test_adversarial_bypass_fix.py` - Bypass analysis
- `tests/integration/test_external_review_validation.py` - Integration tests
- `tests/unit/test_circuit_breaker.py` - Circuit breaker tests
- `tests/unit/test_adapter_health.py` - Adapter health tests

### Documentation

- `docs/CRITICAL_ISSUES_REGISTER.md` - Critical issues tracking
- `docs/TEST_RESULTS_SUMMARY.md` - Test results summary
- `docs/EXTERNAL_REVIEW_RESPONSE.md` - External review response
- `ROADMAP.md` - 4-phase roadmap
- `README.md` - Project overview

---

## References

- **Critical Issues:** `docs/CRITICAL_ISSUES_REGISTER.md`
- **Roadmap:** `ROADMAP.md`
- **Test Results:** `docs/TEST_RESULTS_SUMMARY.md`
- **External Review:** `docs/EXTERNAL_REVIEW_RESPONSE.md`
- **Adversarial Suite:** `data/gpt5_adversarial_suite.jsonl`

---

## Conclusion

The LLM Security Firewall project has a solid technical foundation with hexagonal architecture and core security features operational. Critical security fixes have been implemented for zero-width Unicode, RLO/Bidi, and concatenation bypasses. However, significant gaps remain:

- 32/34 high+critical severity adversarial bypasses unaddressed
- Fail-open behavior on cache failures (security violation)
- Memory usage exceeds limits (4.5x)
- Test coverage claims unverified
- CI/CD gates not enforced

**Recommendation:** Prioritize Phase 1 activities (stabilization and security hardening) before declaring production readiness. Immediate focus should be on adversarial bypass resolution, fail-safe implementation, and memory optimization.

**Status:** Release Candidate - Not Production Ready
**Next Review:** Weekly during Phase 1, monthly thereafter

---

**Last Updated:** 2025-12-01
**Document Version:** 1.0
