# 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. from __future__ import absolute_import, division, print_function import struct from cryptography import utils from cryptography.exceptions import ( AlreadyFinalized, InvalidKey, UnsupportedAlgorithm, _Reasons, ) from cryptography.hazmat.backends import _get_backend from cryptography.hazmat.backends.interfaces import HashBackend from cryptography.hazmat.primitives import constant_time, hashes from cryptography.hazmat.primitives.kdf import KeyDerivationFunction def _int_to_u32be(n): return struct.pack(">I", n) @utils.register_interface(KeyDerivationFunction) class X963KDF(object): def __init__(self, algorithm, length, sharedinfo, backend=None): backend = _get_backend(backend) max_len = algorithm.digest_size * (2 ** 32 - 1) if length > max_len: raise ValueError( "Can not derive keys larger than {} bits.".format(max_len) ) if sharedinfo is not None: utils._check_bytes("sharedinfo", sharedinfo) self._algorithm = algorithm self._length = length self._sharedinfo = sharedinfo if not isinstance(backend, HashBackend): raise UnsupportedAlgorithm( "Backend object does not implement HashBackend.", _Reasons.BACKEND_MISSING_INTERFACE, ) self._backend = backend self._used = False def derive(self, key_material): if self._used: raise AlreadyFinalized self._used = True utils._check_byteslike("key_material", key_material) output = [b""] outlen = 0 counter = 1 while self._length > outlen: h = hashes.Hash(self._algorithm, self._backend) h.update(key_material) h.update(_int_to_u32be(counter)) if self._sharedinfo is not None: h.update(self._sharedinfo) output.append(h.finalize()) outlen += len(output[-1]) counter += 1 return b"".join(output)[: self._length] def verify(self, key_material, expected_key): if not constant_time.bytes_eq(self.derive(key_material), expected_key): raise InvalidKey