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# 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.
import base64
import binascii
import os
import struct
import time
import typing
from cryptography import utils
from cryptography.exceptions import InvalidSignature
from cryptography.hazmat.backends import _get_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: bytes, backend=None):
backend = _get_backend(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) -> bytes:
return base64.urlsafe_b64encode(os.urandom(32))
def encrypt(self, data: bytes) -> bytes:
return self.encrypt_at_time(data, int(time.time()))
def encrypt_at_time(self, data: bytes, current_time: int) -> bytes:
iv = os.urandom(16)
return self._encrypt_from_parts(data, current_time, iv)
def _encrypt_from_parts(
self, data: bytes, current_time: int, iv: bytes
) -> bytes:
utils._check_bytes("data", data)
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: bytes, ttl: typing.Optional[int] = None) -> bytes:
timestamp, data = Fernet._get_unverified_token_data(token)
if ttl is None:
time_info = None
else:
time_info = (ttl, int(time.time()))
return self._decrypt_data(data, timestamp, time_info)
def decrypt_at_time(
self, token: bytes, ttl: int, current_time: int
) -> bytes:
if ttl is None:
raise ValueError(
"decrypt_at_time() can only be used with a non-None ttl"
)
timestamp, data = Fernet._get_unverified_token_data(token)
return self._decrypt_data(data, timestamp, (ttl, current_time))
def extract_timestamp(self, token: bytes) -> int:
timestamp, data = Fernet._get_unverified_token_data(token)
# Verify the token was not tampered with.
self._verify_signature(data)
return timestamp
@staticmethod
def _get_unverified_token_data(token: bytes) -> typing.Tuple[int, bytes]:
utils._check_bytes("token", token)
try:
data = base64.urlsafe_b64decode(token)
except (TypeError, binascii.Error):
raise InvalidToken
if not data or data[0] != 0x80:
raise InvalidToken
try:
(timestamp,) = struct.unpack(">Q", data[1:9])
except struct.error:
raise InvalidToken
return timestamp, data
def _verify_signature(self, data: bytes) -> None:
h = HMAC(self._signing_key, hashes.SHA256(), backend=self._backend)
h.update(data[:-32])
try:
h.verify(data[-32:])
except InvalidSignature:
raise InvalidToken
def _decrypt_data(
self,
data: bytes,
timestamp: int,
time_info: typing.Optional[typing.Tuple[int, int]],
) -> bytes:
if time_info is not None:
ttl, current_time = time_info
if timestamp + ttl < current_time:
raise InvalidToken
if current_time + _MAX_CLOCK_SKEW < timestamp:
raise InvalidToken
self._verify_signature(data)
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: typing.Iterable[Fernet]):
fernets = list(fernets)
if not fernets:
raise ValueError(
"MultiFernet requires at least one Fernet instance"
)
self._fernets = fernets
def encrypt(self, msg: bytes) -> bytes:
return self.encrypt_at_time(msg, int(time.time()))
def encrypt_at_time(self, msg: bytes, current_time: int) -> bytes:
return self._fernets[0].encrypt_at_time(msg, current_time)
def rotate(self, msg: bytes) -> bytes:
timestamp, data = Fernet._get_unverified_token_data(msg)
for f in self._fernets:
try:
p = f._decrypt_data(data, timestamp, None)
break
except InvalidToken:
pass
else:
raise InvalidToken
iv = os.urandom(16)
return self._fernets[0]._encrypt_from_parts(p, timestamp, iv)
def decrypt(self, msg: bytes, ttl: typing.Optional[int] = None) -> bytes:
for f in self._fernets:
try:
return f.decrypt(msg, ttl)
except InvalidToken:
pass
raise InvalidToken
def decrypt_at_time(
self, msg: bytes, ttl: int, current_time: int
) -> bytes:
for f in self._fernets:
try:
return f.decrypt_at_time(msg, ttl, current_time)
except InvalidToken:
pass
raise InvalidToken
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