| # 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 six |
| |
| 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.primitives import constant_time, hmac |
| from cryptography.hazmat.primitives.kdf import KeyDerivationFunction |
| |
| |
| @utils.register_interface(KeyDerivationFunction) |
| class HKDF(object): |
| def __init__(self, algorithm, length, salt, info, backend=None): |
| backend = _get_backend(backend) |
| if not isinstance(backend, HMACBackend): |
| raise UnsupportedAlgorithm( |
| "Backend object does not implement HMACBackend.", |
| _Reasons.BACKEND_MISSING_INTERFACE, |
| ) |
| |
| self._algorithm = algorithm |
| |
| if salt is None: |
| salt = b"\x00" * self._algorithm.digest_size |
| else: |
| utils._check_bytes("salt", salt) |
| |
| self._salt = salt |
| |
| self._backend = backend |
| |
| self._hkdf_expand = HKDFExpand(self._algorithm, length, info, backend) |
| |
| def _extract(self, key_material): |
| h = hmac.HMAC(self._salt, self._algorithm, backend=self._backend) |
| h.update(key_material) |
| return h.finalize() |
| |
| def derive(self, key_material): |
| utils._check_byteslike("key_material", key_material) |
| return self._hkdf_expand.derive(self._extract(key_material)) |
| |
| 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 HKDFExpand(object): |
| def __init__(self, algorithm, length, info, backend=None): |
| backend = _get_backend(backend) |
| if not isinstance(backend, HMACBackend): |
| raise UnsupportedAlgorithm( |
| "Backend object does not implement HMACBackend.", |
| _Reasons.BACKEND_MISSING_INTERFACE, |
| ) |
| |
| self._algorithm = algorithm |
| |
| self._backend = backend |
| |
| max_length = 255 * algorithm.digest_size |
| |
| if length > max_length: |
| raise ValueError( |
| "Can not derive keys larger than {} octets.".format(max_length) |
| ) |
| |
| self._length = length |
| |
| if info is None: |
| info = b"" |
| else: |
| utils._check_bytes("info", info) |
| |
| self._info = info |
| |
| self._used = False |
| |
| def _expand(self, key_material): |
| output = [b""] |
| counter = 1 |
| |
| while self._algorithm.digest_size * (len(output) - 1) < self._length: |
| h = hmac.HMAC(key_material, self._algorithm, backend=self._backend) |
| h.update(output[-1]) |
| h.update(self._info) |
| h.update(six.int2byte(counter)) |
| output.append(h.finalize()) |
| counter += 1 |
| |
| return b"".join(output)[: self._length] |
| |
| def derive(self, key_material): |
| utils._check_byteslike("key_material", key_material) |
| if self._used: |
| raise AlreadyFinalized |
| |
| self._used = True |
| return self._expand(key_material) |
| |
| def verify(self, key_material, expected_key): |
| if not constant_time.bytes_eq(self.derive(key_material), expected_key): |
| raise InvalidKey |