| # 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 |