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Diffstat (limited to 'src/cryptography/fernet.py')
-rw-r--r-- | src/cryptography/fernet.py | 150 |
1 files changed, 150 insertions, 0 deletions
diff --git a/src/cryptography/fernet.py b/src/cryptography/fernet.py new file mode 100644 index 00000000..4f98feec --- /dev/null +++ b/src/cryptography/fernet.py @@ -0,0 +1,150 @@ +# 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. + +from __future__ import absolute_import, division, print_function + +import base64 +import binascii +import os +import struct +import time + +import six + +from cryptography.exceptions import InvalidSignature +from cryptography.hazmat.backends import default_backend +from cryptography.hazmat.primitives import hashes, padding +from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes +from cryptography.hazmat.primitives.hmac import HMAC + + +class InvalidToken(Exception): + pass + + +_MAX_CLOCK_SKEW = 60 + + +class Fernet(object): + def __init__(self, key, backend=None): + if backend is None: + backend = default_backend() + + key = base64.urlsafe_b64decode(key) + if len(key) != 32: + raise ValueError( + "Fernet key must be 32 url-safe base64-encoded bytes." + ) + + self._signing_key = key[:16] + self._encryption_key = key[16:] + self._backend = backend + + @classmethod + def generate_key(cls): + return base64.urlsafe_b64encode(os.urandom(32)) + + def encrypt(self, data): + current_time = int(time.time()) + iv = os.urandom(16) + return self._encrypt_from_parts(data, current_time, iv) + + def _encrypt_from_parts(self, data, current_time, iv): + if not isinstance(data, bytes): + raise TypeError("data must be bytes.") + + padder = padding.PKCS7(algorithms.AES.block_size).padder() + padded_data = padder.update(data) + padder.finalize() + encryptor = Cipher( + algorithms.AES(self._encryption_key), modes.CBC(iv), self._backend + ).encryptor() + ciphertext = encryptor.update(padded_data) + encryptor.finalize() + + basic_parts = ( + b"\x80" + struct.pack(">Q", current_time) + iv + ciphertext + ) + + h = HMAC(self._signing_key, hashes.SHA256(), backend=self._backend) + h.update(basic_parts) + hmac = h.finalize() + return base64.urlsafe_b64encode(basic_parts + hmac) + + def decrypt(self, token, ttl=None): + if not isinstance(token, bytes): + raise TypeError("token must be bytes.") + + current_time = int(time.time()) + + try: + data = base64.urlsafe_b64decode(token) + except (TypeError, binascii.Error): + raise InvalidToken + + if not data or six.indexbytes(data, 0) != 0x80: + raise InvalidToken + + try: + timestamp, = struct.unpack(">Q", data[1:9]) + except struct.error: + raise InvalidToken + if ttl is not None: + if timestamp + ttl < current_time: + raise InvalidToken + if current_time + _MAX_CLOCK_SKEW < timestamp: + raise InvalidToken + h = HMAC(self._signing_key, hashes.SHA256(), backend=self._backend) + h.update(data[:-32]) + try: + h.verify(data[-32:]) + except InvalidSignature: + raise InvalidToken + + iv = data[9:25] + ciphertext = data[25:-32] + decryptor = Cipher( + algorithms.AES(self._encryption_key), modes.CBC(iv), self._backend + ).decryptor() + plaintext_padded = decryptor.update(ciphertext) + try: + plaintext_padded += decryptor.finalize() + except ValueError: + raise InvalidToken + unpadder = padding.PKCS7(algorithms.AES.block_size).unpadder() + + unpadded = unpadder.update(plaintext_padded) + try: + unpadded += unpadder.finalize() + except ValueError: + raise InvalidToken + return unpadded + + +class MultiFernet(object): + def __init__(self, fernets): + fernets = list(fernets) + if not fernets: + raise ValueError( + "MultiFernet requires at least one Fernet instance" + ) + self._fernets = fernets + + def encrypt(self, msg): + return self._fernets[0].encrypt(msg) + + def decrypt(self, msg, ttl=None): + for f in self._fernets: + try: + return f.decrypt(msg, ttl) + except InvalidToken: + pass + raise InvalidToken |