# This file is dual licensed under the terms of the Apache License, Version
# 2.0, and the BSD License. See the LICENSE file in the root of this repository
# for complete details.


import abc


class KeyDerivationFunction(metaclass=abc.ABCMeta):
    @abc.abstractmethod
    def derive(self, key_material: bytes) -> bytes:
        """
        Deterministically generates and returns a new key based on the existing
        key material.
        """

    @abc.abstractmethod
    def verify(self, key_material: bytes, expected_key: bytes) -> None:
        """
        Checks whether the key generated by the key material matches the
        expected derived key. Raises an exception if they do not match.
        """