| # Copyright 2019 Google LLC. |
| # |
| # Licensed under the Apache License, Version 2.0 (the "License"); |
| # you may not use this file except in compliance with the License. |
| # You may obtain a copy of the License at |
| # |
| # http://www.apache.org/licenses/LICENSE-2.0 |
| # |
| # Unless required by applicable law or agreed to in writing, software |
| # distributed under the License is distributed on an "AS IS" BASIS, |
| # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| # See the License for the specific language governing permissions and |
| # limitations under the License. |
| |
| """AEAD wrapper.""" |
| |
| from __future__ import absolute_import |
| from __future__ import division |
| from __future__ import google_type_annotations |
| from __future__ import print_function |
| |
| from absl import logging |
| |
| from typing import Type |
| |
| from tink.python.aead import aead |
| from tink.python.core import crypto_format |
| from tink.python.core import primitive_set |
| from tink.python.core import primitive_wrapper |
| from tink.python.core import tink_error |
| |
| |
| class _WrappedAead(aead.Aead): |
| """Implements Aead for a set of Aead primitives.""" |
| |
| def __init__(self, pset: primitive_set.PrimitiveSet): |
| self._primitive_set = pset |
| |
| def encrypt(self, plaintext: bytes, associated_data: bytes) -> bytes: |
| primary = self._primitive_set.primary() |
| return primary.identifier + primary.primitive.encrypt( |
| plaintext, associated_data) |
| |
| def decrypt(self, ciphertext: bytes, associated_data: bytes) -> bytes: |
| if len(ciphertext) > crypto_format.NON_RAW_PREFIX_SIZE: |
| prefix = ciphertext[:crypto_format.NON_RAW_PREFIX_SIZE] |
| ciphertext_no_prefix = ciphertext[crypto_format.NON_RAW_PREFIX_SIZE:] |
| for entry in self._primitive_set.primitive_from_identifier(prefix): |
| try: |
| return entry.primitive.decrypt(ciphertext_no_prefix, |
| associated_data) |
| except tink_error.TinkError as e: |
| logging.info( |
| 'ciphertext prefix matches a key, but cannot decrypt: %s', e) |
| # Let's try all RAW keys. |
| for entry in self._primitive_set.raw_primitives(): |
| try: |
| return entry.primitive.decrypt(ciphertext, associated_data) |
| except tink_error.TinkError as e: |
| pass |
| # nothing works. |
| raise tink_error.TinkError('Decryption failed.') |
| |
| |
| class AeadWrapper(primitive_wrapper.PrimitiveWrapper[aead.Aead]): |
| """AeadWrapper is the implementation of PrimitiveWrapper for Aead. |
| |
| Key rotation works as follows: each ciphertext is prefixed with the keyId. |
| When decrypting, we first try all primitives whose keyId starts with the |
| prefix of the ciphertext. If none of these succeed, we try the raw primitives. |
| If any succeeds, we return the ciphertext, otherwise we simply raise a |
| TinkError. |
| """ |
| |
| def wrap(self, pset: primitive_set.PrimitiveSet) -> aead.Aead: |
| return _WrappedAead(pset) |
| |
| def primitive_class(self) -> Type[aead.Aead]: |
| return aead.Aead |