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Editing: concatkdf.py
# 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 HMACBackend from cryptography.hazmat.backends.interfaces import HashBackend from cryptography.hazmat.primitives import constant_time, hashes, hmac from cryptography.hazmat.primitives.kdf import KeyDerivationFunction def _int_to_u32be(n): return struct.pack(">I", n) def _common_args_checks(algorithm, length, otherinfo): max_length = algorithm.digest_size * (2 ** 32 - 1) if length > max_length: raise ValueError( "Can not derive keys larger than {} bits.".format(max_length) ) if otherinfo is not None: utils._check_bytes("otherinfo", otherinfo) def _concatkdf_derive(key_material, length, auxfn, otherinfo): utils._check_byteslike("key_material", key_material) output = [b""] outlen = 0 counter = 1 while length > outlen: h = auxfn() h.update(_int_to_u32be(counter)) h.update(key_material) h.update(otherinfo) output.append(h.finalize()) outlen += len(output[-1]) counter += 1 return b"".join(output)[:length] @utils.register_interface(KeyDerivationFunction) class ConcatKDFHash(object): def __init__(self, algorithm, length, otherinfo, backend=None): backend = _get_backend(backend) _common_args_checks(algorithm, length, otherinfo) self._algorithm = algorithm self._length = length self._otherinfo = otherinfo if self._otherinfo is None: self._otherinfo = b"" if not isinstance(backend, HashBackend): raise UnsupportedAlgorithm( "Backend object does not implement HashBackend.", _Reasons.BACKEND_MISSING_INTERFACE, ) self._backend = backend self._used = False def _hash(self): return hashes.Hash(self._algorithm, self._backend) def derive(self, key_material): if self._used: raise AlreadyFinalized self._used = True return _concatkdf_derive( key_material, self._length, self._hash, self._otherinfo ) def verify(self, key_material, expected_key): if not constant_time.bytes_eq(self.derive(key_material), expected_key): raise InvalidKey @utils.register_interface(KeyDerivationFunction) class ConcatKDFHMAC(object): def __init__(self, algorithm, length, salt, otherinfo, backend=None): backend = _get_backend(backend) _common_args_checks(algorithm, length, otherinfo) self._algorithm = algorithm self._length = length self._otherinfo = otherinfo if self._otherinfo is None: self._otherinfo = b"" if salt is None: salt = b"\x00" * algorithm.block_size else: utils._check_bytes("salt", salt) self._salt = salt if not isinstance(backend, HMACBackend): raise UnsupportedAlgorithm( "Backend object does not implement HMACBackend.", _Reasons.BACKEND_MISSING_INTERFACE, ) self._backend = backend self._used = False def _hmac(self): return hmac.HMAC(self._salt, self._algorithm, self._backend) def derive(self, key_material): if self._used: raise AlreadyFinalized self._used = True return _concatkdf_derive( key_material, self._length, self._hmac, self._otherinfo ) def verify(self, key_material, expected_key): if not constant_time.bytes_eq(self.derive(key_material), expected_key): raise InvalidKey
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