id: H23 title: 'Cross-implementation agreement is a necessary gate: every arithmetic component is checked against at least one independent implementation' axis: D kind: methodology statement: Pure Python (wp34) agrees with PARI/GP (curve facts), python-ecdsa and libsecp256k1 (ECDSA), the 19 official BIP340 vectors, hashlib (SHA-256), and the Rust engine (ECDLP answers) on every tested instance; discrepancies found during development are logged. motivation: 'Mandate §10: validate custom mathematical code against independent references.' assumptions: None. expected_contribution: Transparent record of the validation layer. related_work:

• wuille2020bip340
• pornin2013rfc6979 possible_counterexamples: Any disagreement (none remained after development; the kangaroo reference initially looped because its hash ignored the retry seed — fixed and logged). verification_strategy: tests/ (pytest) — all must pass. computational_budget: minutes status: evaluated classification: empirical_observation evidence:
• tests/test_core.py
• tests/test_dlp_reference.py verdict: 11 reference tests pass; agreement with 5 independent implementations; two development bugs caught by the gate (kangaroo retry loop, PARI output parsing). commands:
• .venv/bin/python -m pytest -q tests/test_core.py tests/test_dlp_reference.py

# H23 — Cross-implementation agreement is a necessary gate: every arithmetic component is checked against at least one independent implementation

Pure Python (wp34) agrees with PARI/GP (curve facts), python-ecdsa and libsecp256k1 (ECDSA), the 19 official BIP340 vectors, hashlib (SHA-256), and the Rust engine (ECDLP answers) on every tested instance; discrepancies found during development are logged.