| # 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.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): |
| |
| max_len = algorithm.digest_size * (2 ** 32 - 1) |
| if length > max_len: |
| raise ValueError( |
| "Can not derive keys larger than {0} 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 |