BIP-376: add python ref implementation and initial test vectors

bip-0376.mediawiki

@@ -146,11 +146,30 @@ These are new fields added to the existing PSBT format. Because PSBT is designed
 
 == Reference implementation ==
 
-'''''TODO'''''
+A Python reference implementation is provided in [[bip-0376/reference.py|<code>bip-0376/reference.py</code>]].
+It uses the vendored <code>bitcoin_test</code> PSBT components and <code>secp256k1lab</code> test-only secp256k1 implementation from BIP 375.
+
+It demonstrates the Signer behavior specified in this BIP:
+
+* Key derivation using ''d = (b<sub>spend</sub> + tweak) mod n''.
+* Key negation when ''d·G'' has odd y-coordinate.
+* Verification that the resulting x-only public key matches the output key ''P''.
+* BIP 340 signing with the derived key.
 
 === Test vectors ===
 
-'''''TODO'''''
+Machine-readable test vectors are provided in [[bip-0376/test-vectors.json|<code>bip-0376/test-vectors.json</code>]].
+
+The vector set includes:
+
+* Valid signing cases with and without key negation.
+* Invalid cases for output-key mismatch, zero tweaked key, and out-of-range spend key.
+
+The reference implementation can be run against the vectors with:
+
+<pre>
+./bip-0376/reference.py bip-0376/test-vectors.json
+</pre>
 
 == Appendix ==