ecc: add bindings for schnorr sign/verify

and require "schnorrsig" and "extrakeys" modules of libsecp256k1
2 years ago · 44e27ac8b5
5 changed files with 166 additions and 1 deletions
--- a/contrib/android/p4a_recipes/libsecp256k1/init.py
+++ b/contrib/android/p4a_recipes/libsecp256k1/init.py
@ -10,5 +10,8 @@ class LibSecp256k1RecipePinned(LibSecp256k1Recipe):
    url = "https://github.com/bitcoin-core/secp256k1/archive/{version}.zip"
    sha512sum = "64080d7c3345fe8117787e328a09a3b493c38880cabf73d34e472ab0db4cb17ff989689f0c785680bdba39c446dc8a64d34587f4a0797b225c5687d0eb2da607"

+    # TODO: configure needs options:
+    #   --enable-module-extrakeys
+    #   --enable-module-schnorrsig

 recipe = LibSecp256k1RecipePinned()
--- a/contrib/make_libsecp256k1.sh
+++ b/contrib/make_libsecp256k1.sh
@ -52,6 +52,8 @@ info "Building $pkgname..."
            $AUTOCONF_FLAGS \
            --prefix="$here/$pkgname/dist" \
            --enable-module-recovery \
+            --enable-module-extrakeys \
+            --enable-module-schnorrsig \
            --enable-experimental \
            --enable-module-ecdh \
            --disable-benchmark \
--- a/electrum/ecc.py
+++ b/electrum/ecc.py
@ -236,6 +236,7 @@ class ECPubkey(object):
        return self._y

    def _to_libsecp256k1_pubkey_ptr(self):
+        """pointer to `secp256k1_pubkey` C struct"""
        pubkey = create_string_buffer(64)
        public_pair_bytes = self.get_public_key_bytes(compressed=False)
        ret = _libsecp256k1.secp256k1_ec_pubkey_parse(
@ -244,6 +245,16 @@ class ECPubkey(object):
            raise Exception('public key could not be parsed or is invalid')
        return pubkey

+    def _to_libsecp256k1_xonly_pubkey_ptr(self):
+        """pointer to `secp256k1_xonly_pubkey` C struct"""
+        pubkey = create_string_buffer(64)
+        pk_bytes = self.get_public_key_bytes(compressed=True)[1:]
+        ret = _libsecp256k1.secp256k1_xonly_pubkey_parse(
+            _libsecp256k1.ctx, pubkey, pk_bytes)
+        if 1 != ret:
+            raise Exception('public key could not be parsed or is invalid')
+        return pubkey
+
    @classmethod
    def _from_libsecp256k1_pubkey_ptr(cls, pubkey) -> 'ECPubkey':
        pubkey_serialized = create_string_buffer(65)
@ -341,6 +352,17 @@ class ECPubkey(object):
            return False
        return True

+    def verify_message_schnorr(self, sig64: bytes, msg32: bytes) -> bool:
+        assert isinstance(sig64, bytes), type(sig64)
+        assert len(sig64) == 64, len(sig64)
+        assert isinstance(msg32, bytes), type(msg32)
+        assert len(msg32) == 32, len(msg32)
+        msglen = 32
+        pubkey = self._to_libsecp256k1_xonly_pubkey_ptr()
+        if 1 != _libsecp256k1.secp256k1_schnorrsig_verify(_libsecp256k1.ctx, sig64, msg32, msglen, pubkey):
+            return False
+        return True
+
    def encrypt_message(self, message: bytes, magic: bytes = b'BIE1') -> bytes:
        """
        ECIES encryption/decryption methods; AES-128-CBC with PKCS7 is used as the cipher; hmac-sha256 is used as the mac
@ -501,6 +523,30 @@ class ECPrivkey(ECPubkey):
        sig = sigencode(r, s)
        return sig

+    def sign_schnorr(self, msg32: bytes, *, aux_rand32: bytes = None) -> bytes:
+        assert isinstance(msg32, bytes), type(msg32)
+        assert len(msg32) == 32, len(msg32)
+        if aux_rand32 is None:
+            aux_rand32 = bytes(32)
+        assert isinstance(aux_rand32, bytes), type(aux_rand32)
+        assert len(aux_rand32) == 32, len(aux_rand32)
+        # construct "keypair" obj
+        privkey_bytes = self.secret_scalar.to_bytes(32, byteorder="big")
+        keypair = create_string_buffer(96)
+        ret = _libsecp256k1.secp256k1_keypair_create(_libsecp256k1.ctx, keypair, privkey_bytes)
+        if 1 != ret:
+            raise Exception('secret key was invalid')
+        # sign msg and verify sig
+        sig64 = create_string_buffer(64)
+        ret = _libsecp256k1.secp256k1_schnorrsig_sign32(
+            _libsecp256k1.ctx, sig64, msg32, keypair, aux_rand32)
+        sig64 = bytes(sig64)
+        if 1 != ret:
+            raise Exception('signing failure')
+        if not self.verify_message_schnorr(sig64, msg32):
+            raise Exception("sanity check failed: signature we just created does not verify!")
+        return sig64
+
    def sign_transaction(self, hashed_preimage: bytes) -> bytes:
        return self.sign(hashed_preimage, sigencode=der_sig_from_r_and_s)

--- a/electrum/ecc_fast.py
+++ b/electrum/ecc_fast.py
@ -1,4 +1,9 @@
-# taken (with minor modifications) from pycoin
+# Copyright (c) 2013-2018 Richard Kiss
+# Copyright (c) 2018-2024 The Electrum developers
+# Distributed under the MIT software license, see the accompanying
+# file LICENCE or http://www.opensource.org/licenses/mit-license.php
+#
+# Originally based on pycoin:
 # https://github.com/richardkiss/pycoin/blob/01b1787ed902df23f99a55deb00d8cd076a906fe/pycoin/ecdsa/native/secp256k1.py

 import os
@ -127,6 +132,31 @@ def load_library():
            raise LibModuleMissing('libsecp256k1 library found but it was built '
                                   'without required module (--enable-module-recovery)')

+        # --enable-module-schnorrsig
+        try:
+            secp256k1.secp256k1_schnorrsig_sign32.argtypes = [c_void_p, c_char_p, c_char_p, c_char_p, c_char_p]
+            secp256k1.secp256k1_schnorrsig_sign32.restype = c_int
+
+            secp256k1.secp256k1_schnorrsig_verify.argtypes = [c_void_p, c_char_p, c_char_p, c_size_t, c_char_p]
+            secp256k1.secp256k1_schnorrsig_verify.restype = c_int
+        except (OSError, AttributeError):
+            raise LibModuleMissing('libsecp256k1 library found but it was built '
+                                   'without required module (--enable-module-schnorrsig)')
+
+        # --enable-module-extrakeys
+        try:
+            secp256k1.secp256k1_xonly_pubkey_parse.argtypes = [c_void_p, c_char_p, c_char_p]
+            secp256k1.secp256k1_xonly_pubkey_parse.restype = c_int
+
+            secp256k1.secp256k1_xonly_pubkey_serialize.argtypes = [c_void_p, c_char_p, c_char_p]
+            secp256k1.secp256k1_xonly_pubkey_serialize.restype = c_int
+
+            secp256k1.secp256k1_keypair_create.argtypes = [c_void_p, c_char_p, c_char_p]
+            secp256k1.secp256k1_keypair_create.restype = c_int
+        except (OSError, AttributeError):
+            raise LibModuleMissing('libsecp256k1 library found but it was built '
+                                   'without required module (--enable-module-extrakeys)')
+
        secp256k1.ctx = secp256k1.secp256k1_context_create(SECP256K1_CONTEXT_SIGN | SECP256K1_CONTEXT_VERIFY)
        ret = secp256k1.secp256k1_context_randomize(secp256k1.ctx, os.urandom(32))
        if not ret:
--- a/tests/test_ecc.py
+++ b/tests/test_ecc.py
@ -0,0 +1,84 @@
+import csv
+import io
+
+from electrum import ecc
+from electrum.ecc import ECPubkey, ECPrivkey
+from electrum.crypto import sha256
+
+from . import ElectrumTestCase
+
+
+# note: lots of ecc-related tests are in test_bitcoin.py.
+
+class TestSchnorr(ElectrumTestCase):
+
+    def test_vectors_from_bip0340(self):
+        bip0340_vectors = """index,secret key,public key,aux_rand,message,signature,verification result,comment
+0,0000000000000000000000000000000000000000000000000000000000000003,F9308A019258C31049344F85F89D5229B531C845836F99B08601F113BCE036F9,0000000000000000000000000000000000000000000000000000000000000000,0000000000000000000000000000000000000000000000000000000000000000,E907831F80848D1069A5371B402410364BDF1C5F8307B0084C55F1CE2DCA821525F66A4A85EA8B71E482A74F382D2CE5EBEEE8FDB2172F477DF4900D310536C0,TRUE,
+1,B7E151628AED2A6ABF7158809CF4F3C762E7160F38B4DA56A784D9045190CFEF,DFF1D77F2A671C5F36183726DB2341BE58FEAE1DA2DECED843240F7B502BA659,0000000000000000000000000000000000000000000000000000000000000001,243F6A8885A308D313198A2E03707344A4093822299F31D0082EFA98EC4E6C89,6896BD60EEAE296DB48A229FF71DFE071BDE413E6D43F917DC8DCF8C78DE33418906D11AC976ABCCB20B091292BFF4EA897EFCB639EA871CFA95F6DE339E4B0A,TRUE,
+2,C90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B14E5C9,DD308AFEC5777E13121FA72B9CC1B7CC0139715309B086C960E18FD969774EB8,C87AA53824B4D7AE2EB035A2B5BBBCCC080E76CDC6D1692C4B0B62D798E6D906,7E2D58D8B3BCDF1ABADEC7829054F90DDA9805AAB56C77333024B9D0A508B75C,5831AAEED7B44BB74E5EAB94BA9D4294C49BCF2A60728D8B4C200F50DD313C1BAB745879A5AD954A72C45A91C3A51D3C7ADEA98D82F8481E0E1E03674A6F3FB7,TRUE,
+3,0B432B2677937381AEF05BB02A66ECD012773062CF3FA2549E44F58ED2401710,25D1DFF95105F5253C4022F628A996AD3A0D95FBF21D468A1B33F8C160D8F517,FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF,FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF,7EB0509757E246F19449885651611CB965ECC1A187DD51B64FDA1EDC9637D5EC97582B9CB13DB3933705B32BA982AF5AF25FD78881EBB32771FC5922EFC66EA3,TRUE,test fails if msg is reduced modulo p or n
+4,,D69C3509BB99E412E68B0FE8544E72837DFA30746D8BE2AA65975F29D22DC7B9,,4DF3C3F68FCC83B27E9D42C90431A72499F17875C81A599B566C9889B9696703,00000000000000000000003B78CE563F89A0ED9414F5AA28AD0D96D6795F9C6376AFB1548AF603B3EB45C9F8207DEE1060CB71C04E80F593060B07D28308D7F4,TRUE,
+5,,EEFDEA4CDB677750A420FEE807EACF21EB9898AE79B9768766E4FAA04A2D4A34,,243F6A8885A308D313198A2E03707344A4093822299F31D0082EFA98EC4E6C89,6CFF5C3BA86C69EA4B7376F31A9BCB4F74C1976089B2D9963DA2E5543E17776969E89B4C5564D00349106B8497785DD7D1D713A8AE82B32FA79D5F7FC407D39B,FALSE,public key not on the curve
+6,,DFF1D77F2A671C5F36183726DB2341BE58FEAE1DA2DECED843240F7B502BA659,,243F6A8885A308D313198A2E03707344A4093822299F31D0082EFA98EC4E6C89,FFF97BD5755EEEA420453A14355235D382F6472F8568A18B2F057A14602975563CC27944640AC607CD107AE10923D9EF7A73C643E166BE5EBEAFA34B1AC553E2,FALSE,has_even_y(R) is false
+7,,DFF1D77F2A671C5F36183726DB2341BE58FEAE1DA2DECED843240F7B502BA659,,243F6A8885A308D313198A2E03707344A4093822299F31D0082EFA98EC4E6C89,1FA62E331EDBC21C394792D2AB1100A7B432B013DF3F6FF4F99FCB33E0E1515F28890B3EDB6E7189B630448B515CE4F8622A954CFE545735AAEA5134FCCDB2BD,FALSE,negated message
+8,,DFF1D77F2A671C5F36183726DB2341BE58FEAE1DA2DECED843240F7B502BA659,,243F6A8885A308D313198A2E03707344A4093822299F31D0082EFA98EC4E6C89,6CFF5C3BA86C69EA4B7376F31A9BCB4F74C1976089B2D9963DA2E5543E177769961764B3AA9B2FFCB6EF947B6887A226E8D7C93E00C5ED0C1834FF0D0C2E6DA6,FALSE,negated s value
+9,,DFF1D77F2A671C5F36183726DB2341BE58FEAE1DA2DECED843240F7B502BA659,,243F6A8885A308D313198A2E03707344A4093822299F31D0082EFA98EC4E6C89,0000000000000000000000000000000000000000000000000000000000000000123DDA8328AF9C23A94C1FEECFD123BA4FB73476F0D594DCB65C6425BD186051,FALSE,sG - eP is infinite. Test fails in single verification if has_even_y(inf) is defined as true and x(inf) as 0
+10,,DFF1D77F2A671C5F36183726DB2341BE58FEAE1DA2DECED843240F7B502BA659,,243F6A8885A308D313198A2E03707344A4093822299F31D0082EFA98EC4E6C89,00000000000000000000000000000000000000000000000000000000000000017615FBAF5AE28864013C099742DEADB4DBA87F11AC6754F93780D5A1837CF197,FALSE,sG - eP is infinite. Test fails in single verification if has_even_y(inf) is defined as true and x(inf) as 1
+11,,DFF1D77F2A671C5F36183726DB2341BE58FEAE1DA2DECED843240F7B502BA659,,243F6A8885A308D313198A2E03707344A4093822299F31D0082EFA98EC4E6C89,4A298DACAE57395A15D0795DDBFD1DCB564DA82B0F269BC70A74F8220429BA1D69E89B4C5564D00349106B8497785DD7D1D713A8AE82B32FA79D5F7FC407D39B,FALSE,sig[0:32] is not an X coordinate on the curve
+12,,DFF1D77F2A671C5F36183726DB2341BE58FEAE1DA2DECED843240F7B502BA659,,243F6A8885A308D313198A2E03707344A4093822299F31D0082EFA98EC4E6C89,FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC2F69E89B4C5564D00349106B8497785DD7D1D713A8AE82B32FA79D5F7FC407D39B,FALSE,sig[0:32] is equal to field size
+13,,DFF1D77F2A671C5F36183726DB2341BE58FEAE1DA2DECED843240F7B502BA659,,243F6A8885A308D313198A2E03707344A4093822299F31D0082EFA98EC4E6C89,6CFF5C3BA86C69EA4B7376F31A9BCB4F74C1976089B2D9963DA2E5543E177769FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141,FALSE,sig[32:64] is equal to curve order
+14,,FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC30,,243F6A8885A308D313198A2E03707344A4093822299F31D0082EFA98EC4E6C89,6CFF5C3BA86C69EA4B7376F31A9BCB4F74C1976089B2D9963DA2E5543E17776969E89B4C5564D00349106B8497785DD7D1D713A8AE82B32FA79D5F7FC407D39B,FALSE,public key is not a valid X coordinate because it exceeds the field size
+"""
+        with io.StringIO(bip0340_vectors) as f:
+            csvreader = csv.reader(f)
+            next(csvreader)  # skip first line
+            for idx, seckey, pubkey, aux_rand, message, signature, expected_res, comment in csvreader:
+                idx = int(idx)
+                with self.subTest(msg=f"{idx=}"):
+                    try:
+                        pubkey = ECPubkey(bytes.fromhex("02" + pubkey))
+                    except ecc.InvalidECPointException:
+                        if idx in (5, 14, ):  # expected for these tests
+                            continue
+                        raise
+                    msg32 = bytes.fromhex(message)
+                    signature = bytes.fromhex(signature)
+                    if seckey:
+                        seckey = ECPrivkey(bytes.fromhex(seckey))
+                        aux_rand = bytes.fromhex(aux_rand)
+                        sig_created = seckey.sign_schnorr(msg32, aux_rand32=aux_rand)
+                        self.assertEqual(signature, sig_created)
+                    is_sig_good = pubkey.verify_message_schnorr(signature, msg32)
+                    expected_res = True if expected_res == "TRUE" else False
+                    self.assertEqual(expected_res, is_sig_good)
+
+    def test_sign_schnorr_aux_rand(self):
+        seckey = ECPrivkey(bytes.fromhex("B7E151628AED2A6ABF7158809CF4F3C762E7160F38B4DA56A784D9045190CFEF"))
+        msg32 = sha256("hello there")
+        sig1 = seckey.sign_schnorr(msg32, aux_rand32=None)
+        sig2 = seckey.sign_schnorr(msg32, aux_rand32=b"\x00" * 32)
+        self.assertEqual(sig1, sig2)
+        sig3 = seckey.sign_schnorr(msg32, aux_rand32=bytes(range(32)))
+        self.assertNotEqual(sig1, sig3)
+
+    def test_y_parity_malleability(self):
+        # BIP-0340 says:
+        # > A hypothetical verification algorithm that treats points as public keys,
+        # > and takes the point P directly as input would fail any time a point with
+        # > odd Y is used. While it is possible to correct for this by negating points
+        # > with odd Y coordinate before further processing, this would result in a scheme
+        # > where every (message, signature) pair is valid for two public keys (a type of
+        # > malleability that exists for ECDSA as well, but we don't wish to retain).
+        # > We avoid these problems by treating just the X coordinate as public key.
+        #
+        # As the API in ecc.py treats points as public keys, this malleability exists here:
+        seckey = ECPrivkey.from_secret_scalar(1337)
+        pubkey1 = ECPubkey(seckey.get_public_key_bytes())
+        pubkey2 = ecc.CURVE_ORDER * ecc.GENERATOR + (-1) * pubkey1
+        self.assertNotEqual(pubkey1.get_public_key_bytes(True), pubkey2.get_public_key_bytes(True))
+        self.assertEqual(pubkey1.get_public_key_bytes(True)[1:], pubkey2.get_public_key_bytes(True)[1:])
+        msg32 = sha256("hello there")
+        sig = seckey.sign_schnorr(msg32, aux_rand32=None)
+        self.assertTrue(pubkey1.verify_message_schnorr(sig, msg32))
+        self.assertTrue(pubkey2.verify_message_schnorr(sig, msg32))