ADR-050: Quality Engineering Response — Security Hardening & Code Quality

Field	Value
Status	Accepted
Date	2026-03-06
Deciders	ruv
Depends on	ADR-032 (Multistatic Mesh Security)
Issue	#170

Context

An independent quality engineering analysis (issue #170) identified 7 critical findings across the Rust codebase. After verification against the source code, the following findings are confirmed and require action:

Confirmed Critical Findings

#	Finding	Location	Verified
1	Fake HMAC in secure_tdm.rs — XOR fold with hardcoded key	hardware/src/esp32/secure_tdm.rs:253	YES — comments say "sufficient for testing"
2	sensing-server/main.rs is 3,741 lines — CC=65, god object	sensing-server/src/main.rs	YES — confirmed 3,741 lines
3	WebSocket server has zero authentication	Rust WS codebase	YES — no auth/token checks found
4	Zero security tests in Rust codebase	Entire workspace	YES — no auth/injection/tampering tests
5	54K fps claim has no supporting benchmark	No criterion benchmarks	YES — no benchmarks exist

Findings Requiring Further Investigation

#	Finding	Status
6	Unauthenticated OTA firmware endpoint	Not found in Rust code — may be ESP32 C firmware level
7	WASM upload without mandatory signatures	Needs review of WASM loader
8	O(n^2) autocorrelation in heart rate detection	Needs profiling to confirm impact

Decision

Address findings in 3 priority sprints as recommended by the report.

Sprint 1: Security (Blocks Deployment)

1. Replace fake HMAC with real HMAC-SHA256 in secure_tdm.rs

   • Use the hmac + sha2 crates (already in Cargo.lock)
   • Remove XOR fold implementation
   • Add key derivation (no more hardcoded keys)

2. Add WebSocket authentication

   • Token-based auth on WS upgrade handshake
   • Optional API key for local-network deployments
   • Configurable via environment variable

3. Add security test suite

   • Auth bypass attempts
   • Malformed CSI frame injection
   • Protocol tampering (TDM beacon replay, nonce reuse)

Sprint 2: Code Quality & Testability

4. Decompose main.rs (3,741 lines -> ~14 focused modules)

   • Extract HTTP routes, WebSocket handler, CSI pipeline, config, state
   • Target: no file over 500 lines

5. Add criterion benchmarks

   • CSI frame parsing throughput
   • Signal processing pipeline latency
   • WebSocket broadcast fanout

Sprint 3: Functional Verification

6. Vital sign accuracy verification

   • Reference signal tests with known BPM
   • False-negative rate measurement

7. Fix O(n^2) autocorrelation (if confirmed by profiling)

   • Replace brute-force lag with FFT-based autocorrelation

Consequences

Positive

• Addresses all critical security findings before any production deployment
• main.rs decomposition enables unit testing of server components
• Criterion benchmarks provide verifiable performance claims
• Security test suite prevents regression

Negative

• Sprint 1 security changes are breaking for any existing TDM mesh deployments (fake HMAC -> real HMAC requires firmware update)
• main.rs decomposition is a large refactor with merge conflict risk

Neutral

• The report correctly identifies that life-safety claims (disaster detection, vital signs) require rigorous verification — this is an ongoing process, not a single sprint

Acknowledgment

Thanks to @proffesor-for-testing for the thorough 10-report analysis. The full report is archived at the original gist.

References

• Issue #170: Quality Engineering Analysis
• ADR-032: Multistatic Mesh Security Hardening
• ADR-028: ESP32 Capability Audit