rsa.py 文件源码

def calculate_cost(self):
        """Calculate the cost of fulfilling self condition.

        The cost of the RSA condition is the size of the modulus
        squared, divided By 64.

        Returns:
            int: Expected maximum cost to fulfill self condition.

        """
        if self.modulus is None:
            raise MissingDataError('Requires a public modulus')

        public_numbers = RSAPublicNumbers(
            PUBLIC_EXPONENT,
            int.from_bytes(self.modulus, byteorder='big'),
        )
        public_key = public_numbers.public_key(default_backend())
        modulus_bit_length = public_key.key_size
        # TODO watch out >> in Python is not the sane as JS >>>, may need to be
        # corrected. For instance see:
        # http://grokbase.com/t/python/python-list/0454t3tgaw/zero-fill-shift
        return int(math.pow(modulus_bit_length, 2)) >> RsaSha256.COST_RIGHT_SHIFT