investigate: ecdsa created signatures do not validate with coincurve

[eukreign]

Investigate why old signatures created using ecdsa do not validate with coincurve:

Old signing code (private_key in this case is instance of ecdsa.SigningKey):

lbry-sdk/lbry/wallet/transaction.py

Line 459 in 26d0e87

self.signable.signature = channel.private_key.sign_digest_deterministic(digest, hashfunc=hashlib.sha256)

New signing code (calls the libsecp256k1 code wrapped by coincurve):

lbry-sdk/lbry/wallet/bip32.py

Lines 238 to 258 in 8076000

	def sign_compact(self, digest):
	""" Produce a compact signature. """
	key = self.signing_key
	signature = libsecp256k1_ffi.new('secp256k1_ecdsa_signature *')
	signed = libsecp256k1.secp256k1_ecdsa_sign(
	key.context.ctx, signature, digest, key.secret,
	libsecp256k1_ffi.NULL, libsecp256k1_ffi.NULL
	)
	if not signed:
	raise ValueError('The private key was invalid.')
	serialized = libsecp256k1_ffi.new('unsigned char[%d]' % CDATA_SIG_LENGTH)
	compacted = libsecp256k1.secp256k1_ecdsa_signature_serialize_compact(
	key.context.ctx, serialized, signature
	)
	if compacted != 1:
	raise ValueError('The signature could not be compacted.')
	return bytes(libsecp256k1_ffi.buffer(serialized, CDATA_SIG_LENGTH))

New validation code includes the old validation as fallback for old signatures:

lbry-sdk/lbry/wallet/transaction.py

Lines 428 to 440 in 8076000

	def is_signature_valid(signature, digest, public_key_bytes):
	signature = cdata_to_der(deserialize_compact(signature))
	public_key = cPublicKey(public_key_bytes)
	is_valid = public_key.verify(signature, digest, None)
	if not is_valid: # try old way
	# ytsync signed claims don't seem to validate with coincurve
	try:
	pk = ec.EllipticCurvePublicKey.from_encoded_point(ec.SECP256K1(), public_key_bytes)
	pk.verify(signature, digest, ec.ECDSA(Prehashed(hashes.SHA256())))
	return True
	except (ValueError, InvalidSignature):
	pass
	return is_valid

The following tests illustrate the problem, if you step through debugger you will see that it does not validate with coincurve and instead falls back to using the old validation with cryptography:

Example 1 (older):

lbry-sdk/tests/unit/wallet/test_schema_signing.py

Line 74 in 8076000

def test_signed_claim_made_by_ytsync(self):

Example 2 (much more recent):

lbry-sdk/tests/unit/wallet/test_schema_signing.py

Line 123 in 8076000

def test_another_signed_claim_made_by_ytsync(self):

Why can't coincurve validate those signatures? Is there anything we can do to get it to validate?

One interesting thing to note is that the new signatures do validate with the old validation scheme using cryptography library.

[eukreign]

posted to stackoverflow

https://stackoverflow.com/questions/70477905/why-are-signatures-created-with-ecdsa-python-library-not-valid-with-coincurve