BIP461: add test vectors and reference implementation (#2328)

All vectors were tested against libsecp256k1, and
all verification vectors were checked against OpenSSL.
A check was also added to the `verify` specification
to reject pubkeys with x or y coordinates greater than
or equal to `p`.

bip-0461/run_test_vectors.py

@@ -0,0 +1,59 @@
+"""Run the low-R grinding test vectors."""
+
+import csv
+import os
+import sys
+
+import reference
+
+FILENAME_SIGN_TEST = os.path.join(sys.path[0], 'sign_test_vectors.csv')
+FILENAME_VERIFY_TEST = os.path.join(sys.path[0], 'verify_test_vectors.csv')
+
+def sig_from_hex(s):
+    """Parse a compact signature into the integer pair (r, s)."""
+    b = bytes.fromhex(s)
+    assert len(b) == 64
+    return (int.from_bytes(b[:32], 'big'), int.from_bytes(b[32:], 'big'))
+
+def sig_hex(sig):
+    return (reference.bytes_from_int(sig[0]) + reference.bytes_from_int(sig[1])).hex()
+
+def pubkey_from_hex(s):
+    """Parse an uncompressed SEC 1 public key into a point."""
+    b = bytes.fromhex(s)
+    if b == b'\x00':
+        return None
+    assert len(b) == 65 and b[0] == 0x04
+    return (int.from_bytes(b[1:33], 'big'), int.from_bytes(b[33:], 'big'))
+
+def result_from_str(s):
+    assert s in ('TRUE', 'FALSE')
+    return s == 'TRUE'
+
+with open(FILENAME_SIGN_TEST, newline='', encoding='utf-8') as csvfile:
+    print(f"Running {FILENAME_SIGN_TEST} tests...")
+    reader = csv.DictReader(csvfile)
+    for row in reader:
+        seckey = bytes.fromhex(row['seckey'])
+        msghash = bytes.fromhex(row['msghash'])
+        if row['sig'] == '':
+            # An empty signature means signing must fail for this secret key.
+            raised = False
+            try:
+                reference.deterministic_sign(seckey, msghash)
+            except ValueError:
+                raised = True
+            assert raised
+            continue
+        sig = reference.deterministic_sign(seckey, msghash)
+        assert reference.is_low_r(sig)
+        assert row['sig'] == sig_hex(sig)
+
+with open(FILENAME_VERIFY_TEST, newline='', encoding='utf-8') as csvfile:
+    print(f"Running {FILENAME_VERIFY_TEST} tests...")
+    reader = csv.DictReader(csvfile)
+    for row in reader:
+        pubkey = pubkey_from_hex(row['pubkey'])
+        msghash = bytes.fromhex(row['msghash'])
+        sig = sig_from_hex(row['sig'])
+        assert reference.verify(sig, pubkey, msghash) == result_from_str(row['result'])