secp.py

from secp256k1 import PrivateKey, PublicKey


# We extend the public key to define some operations on points
# Picked from https://github.com/WTRMQDev/secp256k1-zkp-py/blob/master/secp256k1_zkp/__init__.py
class PublicKeyExt(PublicKey):
    def __add__(self, pubkey2):
        if isinstance(pubkey2, PublicKey):
            new_pub = PublicKey()
            new_pub.combine([self.public_key, pubkey2.public_key])
            return new_pub
        else:
            raise TypeError("Cant add pubkey and %s"%pubkey2.__class__)

    def __neg__(self):
        serialized=self.serialize()
        first_byte, remainder = serialized[:1], serialized[1:]
        # flip odd/even byte
        first_byte = {b'\x03':b'\x02', b'\x02':b'\x03'}[first_byte]
        return PublicKey(first_byte+ remainder, raw=True)

    def __sub__(self, pubkey2):
        if isinstance(pubkey2, PublicKey):
            return self + (-pubkey2)
        else:
            raise TypeError("Can't add pubkey and %s"%pubkey2.__class__)
    
    def mult(self, privkey):
        if isinstance(privkey, PrivateKey):
            return self.tweak_mul(privkey.private_key)
        else:
            raise TypeError("Can't multiply with non privatekey")
    
    def __eq__(self, pubkey2):
        if isinstance(pubkey2, PublicKey):
            seq1 = self.to_data()
            seq2 = pubkey2.to_data()
            return seq1 == seq2
        else:
            raise TypeError("Can't compare pubkey and %s" % pubkey2.__class__)
    
    def to_data(self):
        return [self.public_key.data[i] for i in range(64)]


# Horrible monkeypatching
PublicKey.__add__ = PublicKeyExt.__add__
PublicKey.__neg__ = PublicKeyExt.__neg__
PublicKey.__sub__ = PublicKeyExt.__sub__
PublicKey.mult = PublicKeyExt.mult
PublicKey.__eq__ = PublicKeyExt.__eq__
PublicKey.to_data = PublicKeyExt.to_data