JezK
Edit File: 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. import typing from cryptography import utils from cryptography.exceptions import ( AlreadyFinalized, InvalidKey, ) from cryptography.hazmat.primitives import constant_time, hashes, hmac from cryptography.hazmat.primitives.kdf import KeyDerivationFunction def _int_to_u32be(n: int) -> bytes: return n.to_bytes(length=4, byteorder="big") def _common_args_checks( algorithm: hashes.HashAlgorithm, length: int, otherinfo: typing.Optional[bytes], ) -> None: max_length = algorithm.digest_size * (2**32 - 1) if length > max_length: raise ValueError( "Cannot derive keys larger than {} bits.".format(max_length) ) if otherinfo is not None: utils._check_bytes("otherinfo", otherinfo) def _concatkdf_derive( key_material: bytes, length: int, auxfn: typing.Callable[[], hashes.HashContext], otherinfo: bytes, ) -> bytes: 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] class ConcatKDFHash(KeyDerivationFunction): def __init__( self, algorithm: hashes.HashAlgorithm, length: int, otherinfo: typing.Optional[bytes], backend: typing.Any = None, ): _common_args_checks(algorithm, length, otherinfo) self._algorithm = algorithm self._length = length self._otherinfo: bytes = otherinfo if otherinfo is not None else b"" self._used = False def _hash(self) -> hashes.Hash: return hashes.Hash(self._algorithm) def derive(self, key_material: bytes) -> bytes: if self._used: raise AlreadyFinalized self._used = True return _concatkdf_derive( key_material, self._length, self._hash, self._otherinfo ) def verify(self, key_material: bytes, expected_key: bytes) -> None: if not constant_time.bytes_eq(self.derive(key_material), expected_key): raise InvalidKey class ConcatKDFHMAC(KeyDerivationFunction): def __init__( self, algorithm: hashes.HashAlgorithm, length: int, salt: typing.Optional[bytes], otherinfo: typing.Optional[bytes], backend: typing.Any = None, ): _common_args_checks(algorithm, length, otherinfo) self._algorithm = algorithm self._length = length self._otherinfo: bytes = otherinfo if otherinfo is not None else b"" if algorithm.block_size is None: raise TypeError( "{} is unsupported for ConcatKDF".format(algorithm.name) ) if salt is None: salt = b"\x00" * algorithm.block_size else: utils._check_bytes("salt", salt) self._salt = salt self._used = False def _hmac(self) -> hmac.HMAC: return hmac.HMAC(self._salt, self._algorithm) def derive(self, key_material: bytes) -> bytes: if self._used: raise AlreadyFinalized self._used = True return _concatkdf_derive( key_material, self._length, self._hmac, self._otherinfo ) def verify(self, key_material: bytes, expected_key: bytes) -> None: if not constant_time.bytes_eq(self.derive(key_material), expected_key): raise InvalidKey