Add BIP327: MuSig2 for BIP340-compatible Multi-Signatures

Author: jonasnick

README.mediawiki

@@ -1009,6 +1009,13 @@ Those proposing changes should consider that ultimately consent may rest with th
 | Informational
 | Draft
 |-
+| [[bip-0327.mediawiki|327]]
+|
+| MuSig2 for BIP340-compatible Multi-Signatures
+| Jonas Nick, Tim Ruffing, Elliott Jin
+| Informational
+| Draft
+|-
 | [[bip-0329.mediawiki|329]]
 | Applications
 | Wallet Labels Export Format

bip-0327.mediawiki

@@ -0,0 +1,184 @@
+from reference import *
+
+def gen_key_agg_vectors():
+    print("key_agg_vectors.json: Intermediate tweaking result is point at infinity")
+    sk = bytes.fromhex("7FB9E0E687ADA1EEBF7ECFE2F21E73EBDB51A7D450948DFE8D76D7F2D1007671")
+    pk = individual_pk(sk)
+    keygen_ctx = key_agg([pk])
+    aggpoint, _, _ = keygen_ctx
+    aggsk = key_agg_coeff([pk], pk)*int_from_bytes(sk) % n
+    t = n - aggsk
+    assert point_add(point_mul(G, t), aggpoint) == None
+    is_xonly = False
+    tweak = bytes_from_int(t)
+    assert_raises(ValueError, lambda: apply_tweak(keygen_ctx, tweak, is_xonly), lambda e: True)
+    print("  pubkey:", pk.hex().upper())
+    print("  tweak: ", tweak.hex().upper())
+
+def check_sign_verify_vectors():
+    with open(os.path.join(sys.path[0], 'vectors', 'sign_verify_vectors.json')) as f:
+        test_data = json.load(f)
+    X = fromhex_all(test_data["pubkeys"])
+    pnonce = fromhex_all(test_data["pnonces"])
+    aggnonces = fromhex_all(test_data["aggnonces"])
+    msgs = fromhex_all(test_data["msgs"])
+
+    valid_test_cases = test_data["valid_test_cases"]
+    for (i, test_case) in enumerate(valid_test_cases):
+        pubkeys = [X[i] for i in test_case["key_indices"]]
+        pubnonces = [pnonce[i] for i in test_case["nonce_indices"]]
+        aggnonce = aggnonces[test_case["aggnonce_index"]]
+        assert nonce_agg(pubnonces) == aggnonce
+        msg = msgs[test_case["msg_index"]]
+        signer_index = test_case["signer_index"]
+        expected = bytes.fromhex(test_case["expected"])
+
+        session_ctx = SessionContext(aggnonce, pubkeys, [], [], msg)
+        (Q, _, _, _, R, _) = get_session_values(session_ctx)
+        # Make sure the vectors include tests for both variants of Q and R
+        if i == 0:
+           assert has_even_y(Q) and not has_even_y(R)
+        if i == 1:
+           assert not has_even_y(Q) and has_even_y(R)
+        if i == 2:
+           assert has_even_y(Q) and has_even_y(R)
+
+def check_tweak_vectors():
+    with open(os.path.join(sys.path[0], 'vectors', 'tweak_vectors.json')) as f:
+        test_data = json.load(f)
+
+    X = fromhex_all(test_data["pubkeys"])
+    pnonce = fromhex_all(test_data["pnonces"])
+    tweak = fromhex_all(test_data["tweaks"])
+    valid_test_cases = test_data["valid_test_cases"]
+
+    for (i, test_case) in enumerate(valid_test_cases):
+        pubkeys = [X[i] for i in test_case["key_indices"]]
+        tweaks = [tweak[i] for i in test_case["tweak_indices"]]
+        is_xonly = test_case["is_xonly"]
+
+        _, gacc, _ = key_agg_and_tweak(pubkeys, tweaks, is_xonly)
+        # Make sure the vectors include tests for gacc = 1 and -1
+        if i == 0:
+           assert gacc == n - 1
+        if i == 1:
+           assert gacc == 1
+
+def sig_agg_vectors():
+    print("sig_agg_vectors.json:")
+    sk = fromhex_all([
+        "7FB9E0E687ADA1EEBF7ECFE2F21E73EBDB51A7D450948DFE8D76D7F2D1007671",
+        "3874D22DE7A7290C49CE7F1DC17D1A8CD8918E1F799055139D57FC0988D04D10",
+        "D0EA1B84481ED1BCFAA39D6775F97BDC9BF8D7C02FD0C009D6D85BAE5EC7B87A",
+        "FC2BF9E056B273AF0A8AABB815E541A3552C142AC10D4FE584F01D2CAB84F577"])
+    pubkeys = list(map(lambda secret: individual_pk(secret), sk))
+    indices32 = [i.to_bytes(32, 'big') for i in range(6)]
+    secnonces, pnonces = zip(*[nonce_gen_internal(r, None, pubkeys[0], None, None, None) for r in indices32])
+    tweaks = fromhex_all([
+        "B511DA492182A91B0FFB9A98020D55F260AE86D7ECBD0399C7383D59A5F2AF7C",
+        "A815FE049EE3C5AAB66310477FBC8BCCCAC2F3395F59F921C364ACD78A2F48DC",
+        "75448A87274B056468B977BE06EB1E9F657577B7320B0A3376EA51FD420D18A8"])
+    msg = bytes.fromhex("599C67EA410D005B9DA90817CF03ED3B1C868E4DA4EDF00A5880B0082C237869")
+
+    psigs = [None] * 9
+
+    valid_test_cases = [
+        {
+            "aggnonce": None,
+            "nonce_indices": [0, 1],
+            "key_indices": [0, 1],
+            "tweak_indices": [],
+            "is_xonly": [],
+            "psig_indices": [0, 1],
+        }, {
+            "aggnonce": None,
+            "nonce_indices": [0, 2],
+            "key_indices": [0, 2],
+            "tweak_indices": [],
+            "is_xonly": [],
+            "psig_indices": [2, 3],
+        }, {
+            "aggnonce": None,
+            "nonce_indices": [0, 3],
+            "key_indices": [0, 2],
+            "tweak_indices": [0],
+            "is_xonly": [False],
+            "psig_indices": [4, 5],
+        }, {
+            "aggnonce": None,
+            "nonce_indices": [0, 4],
+            "key_indices": [0, 3],
+            "tweak_indices": [0, 1, 2],
+            "is_xonly": [True, False, True],
+            "psig_indices": [6, 7],
+        },
+    ]
+    for (i, test_case) in enumerate(valid_test_cases):
+        is_xonly = test_case["is_xonly"]
+        nonce_indices = test_case["nonce_indices"]
+        key_indices = test_case["key_indices"]
+        psig_indices = test_case["psig_indices"]
+        vec_pnonces = [pnonces[i] for i in nonce_indices]
+        vec_pubkeys = [pubkeys[i] for i in key_indices]
+        vec_tweaks = [tweaks[i] for i in test_case["tweak_indices"]]
+
+        aggnonce = nonce_agg(vec_pnonces)
+        test_case["aggnonce"] = aggnonce.hex().upper()
+        session_ctx = SessionContext(aggnonce, vec_pubkeys, vec_tweaks, is_xonly, msg)
+
+        for j in range(len(key_indices)):
+            # WARNING: An actual implementation should _not_ copy the secnonce.
+            # Reusing the secnonce, as we do here for testing purposes, can leak the
+            # secret key.
+            secnonce_tmp = bytearray(secnonces[nonce_indices[j]][:64] + pubkeys[key_indices[j]])
+            psigs[psig_indices[j]] = sign(secnonce_tmp, sk[key_indices[j]], session_ctx)
+        sig = partial_sig_agg([psigs[i] for i in psig_indices], session_ctx)
+        keygen_ctx = key_agg_and_tweak(vec_pubkeys, vec_tweaks, is_xonly)
+        # To maximize coverage of the sig_agg algorithm, we want one public key
+        # point with an even and one with an odd Y coordinate.
+        if i == 0:
+            assert(has_even_y(keygen_ctx[0]))
+        if i == 1:
+            assert(not has_even_y(keygen_ctx[0]))
+        aggpk = get_xonly_pk(keygen_ctx)
+        assert schnorr_verify(msg, aggpk, sig)
+        test_case["expected"] = sig.hex().upper()
+
+    error_test_case = {
+        "aggnonce": None,
+        "nonce_indices": [0, 4],
+        "key_indices": [0, 3],
+        "tweak_indices": [0, 1, 2],
+        "is_xonly": [True, False, True],
+        "psig_indices": [7, 8],
+        "error": {
+            "type": "invalid_contribution",
+            "signer": 1
+        },
+        "comment": "Partial signature is invalid because it exceeds group size"
+    }
+
+    psigs[8] = bytes.fromhex("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141")
+
+    vec_pnonces = [pnonces[i] for i in error_test_case["nonce_indices"]]
+    aggnonce = nonce_agg(vec_pnonces)
+    error_test_case["aggnonce"] = aggnonce.hex().upper()
+
+    def tohex_all(l):
+        return list(map(lambda e: e.hex().upper(), l))
+
+    print(json.dumps({
+        "pubkeys": tohex_all(pubkeys),
+        "pnonces": tohex_all(pnonces),
+        "tweaks": tohex_all(tweaks),
+        "psigs": tohex_all(psigs),
+        "msg": msg.hex().upper(),
+        "valid_test_cases": valid_test_cases,
+        "error_test_cases": [error_test_case]
+    }, indent=4))
+
+gen_key_agg_vectors()
+check_sign_verify_vectors()
+check_tweak_vectors()
+print()
+sig_agg_vectors()