JezK
Edit File: fernet.py
# 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 time import typing from cryptography import utils from cryptography.exceptions import InvalidSignature 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: def __init__( self, key: typing.Union[bytes, str], backend: typing.Any = None, ): try: key = base64.urlsafe_b64decode(key) except binascii.Error as exc: raise ValueError( "Fernet key must be 32 url-safe base64-encoded bytes." ) from exc 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:] @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), ).encryptor() ciphertext = encryptor.update(padded_data) + encryptor.finalize() basic_parts = ( b"\x80" + current_time.to_bytes(length=8, byteorder="big") + iv + ciphertext ) h = HMAC(self._signing_key, hashes.SHA256()) h.update(basic_parts) hmac = h.finalize() return base64.urlsafe_b64encode(basic_parts + hmac) def decrypt( self, token: typing.Union[bytes, str], 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: typing.Union[bytes, str], 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: typing.Union[bytes, str]) -> 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: typing.Union[bytes, str] ) -> typing.Tuple[int, bytes]: if not isinstance(token, (str, bytes)): raise TypeError("token must be bytes or str") try: data = base64.urlsafe_b64decode(token) except (TypeError, binascii.Error): raise InvalidToken if not data or data[0] != 0x80: raise InvalidToken if len(data) < 9: raise InvalidToken timestamp = int.from_bytes(data[1:9], byteorder="big") return timestamp, data def _verify_signature(self, data: bytes) -> None: h = HMAC(self._signing_key, hashes.SHA256()) 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) ).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: 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: typing.Union[bytes, str]) -> 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: typing.Union[bytes, str], 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: typing.Union[bytes, str], 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