Drop dependency on cryptography library in wallet module

lbry/wallet/bip32.py

@@ -92,6 +92,10 @@ def __init__(self, ledger, pubkey, chain_code, n, depth, parent=None):
         else:
             self.verifying_key = self._verifying_key_from_pubkey(pubkey)
 
+    @classmethod
+    def from_compressed(cls, public_key_bytes, ledger=None) -> 'PublicKey':
+        return cls(ledger, public_key_bytes, bytes((0,)*32), 0, 0)
+
     @classmethod
     def _verifying_key_from_pubkey(cls, pubkey):
         """ Converts a 33-byte compressed pubkey into an coincurve.PublicKey object. """
@@ -137,9 +141,35 @@ def extended_key(self):
             self.pubkey_bytes
         )
 
-    def verify(self, signature, data):
-        """ Produce a signature for piece of data by double hashing it and signing the hash. """
-        return self.verifying_key.verify(signature, data, hasher=double_sha256)
+    def verify(self, signature, digest) -> bool:
+        """ Verify that a signature is valid for a 32 byte digest. """
+
+        if len(signature) != 64:
+            raise ValueError('Signature must be 64 bytes long.')
+
+        if len(digest) != 32:
+            raise ValueError('Digest must be 32 bytes long.')
+
+        key = self.verifying_key
+
+        raw_signature = libsecp256k1_ffi.new('secp256k1_ecdsa_signature *')
+
+        parsed = libsecp256k1.secp256k1_ecdsa_signature_parse_compact(
+            key.context.ctx, raw_signature, signature
+        )
+        assert parsed == 1
+
+        normalized_signature = libsecp256k1_ffi.new('secp256k1_ecdsa_signature *')
+
+        libsecp256k1.secp256k1_ecdsa_signature_normalize(
+            key.context.ctx, normalized_signature, raw_signature
+        )
+
+        verified = libsecp256k1.secp256k1_ecdsa_verify(
+            key.context.ctx, normalized_signature, digest, key.public_key
+        )
+
+        return bool(verified)
 
 
 class PrivateKey(_KeyBase):

lbry/wallet/transaction.py

@@ -4,13 +4,6 @@
 from binascii import hexlify, unhexlify
 from typing import List, Iterable, Optional, Tuple
 
-from coincurve import PublicKey as cPublicKey
-from coincurve.ecdsa import deserialize_compact, cdata_to_der
-from cryptography.hazmat.primitives import hashes
-from cryptography.hazmat.primitives.asymmetric import ec
-from cryptography.hazmat.primitives.asymmetric.utils import Prehashed
-from cryptography.exceptions import InvalidSignature
-
 from lbry.error import InsufficientFundsError
 from lbry.crypto.hash import hash160, sha256
 from lbry.crypto.base58 import Base58
@@ -25,7 +18,7 @@
 from .bcd_data_stream import BCDataStream
 from .hash import TXRef, TXRefImmutable
 from .util import ReadOnlyList
-from .bip32 import PrivateKey
+from .bip32 import PrivateKey, PublicKey
 
 if typing.TYPE_CHECKING:
     from lbry.wallet.account import Account
@@ -426,18 +419,9 @@ def get_signature_digest(self, ledger):
 
     @staticmethod
     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
+        return PublicKey\
+            .from_compressed(public_key_bytes)\
+            .verify(signature, digest)
 
     def is_signed_by(self, channel: 'Output', ledger=None):
         return self.is_signature_valid(