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Fernet.py
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Fernet.py
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# MIT License
#
# Copyright (c) 2022 Mark Qvist / unsigned.io
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
import os
import time
import serial
from RNS.Cryptography import HMAC
from RNS.Cryptography import PKCS7
from RNS.Cryptography.AES import AES_128_CBC
class KryptorHSM:
def __init__(self):
self.serial = serial.Serial('/dev/ttyUSB0', 115200)
def generate_random(self, length):
self.serial.write(b'GENERATE_RANDOM' + length.to_bytes(2, 'big'))
return self.serial.read(length)
def camellia_encrypt(self, plaintext, key, iv):
command = b'CAMELLIA_ENCRYPT' + key + iv + plaintext
self.serial.write(command)
return self.serial.read(len(plaintext))
def camellia_decrypt(self, ciphertext, key, iv):
command = b'CAMELLIA_DECRYPT' + key + iv + ciphertext
self.serial.write(command)
return self.serial.read(len(ciphertext))
def hmac(self, key, data):
command = b'HMAC' + key + data
self.serial.write(command)
return self.serial.read(32)
kryptor_hsm = KryptorHSM()
class Fernet():
FERNET_OVERHEAD = 48
@staticmethod
def generate_key():
return kryptor_hsm.generate_random(32)
def __init__(self, key=None):
if key is None:
raise ValueError("Token key cannot be None")
if len(key) != 32:
raise ValueError("Token key must be 32 bytes, not "+str(len(key)))
self._signing_key = key[:16]
self._encryption_key = key[16:]
def verify_hmac(self, token):
if len(token) <= 32:
raise ValueError("Cannot verify HMAC on token of only "+str(len(token))+" bytes")
else:
received_hmac = token[-32:]
expected_hmac = kryptor_hsm.hmac(self._signing_key, token[:-32])
return received_hmac == expected_hmac
def encrypt(self, data=None):
iv = kryptor_hsm.generate_random(16)
if not isinstance(data, bytes):
raise TypeError("Token plaintext input must be bytes")
try:
ciphertext = kryptor_hsm.camellia_encrypt(
plaintext=PKCS7.pad(data),
key=self._encryption_key,
iv=iv,
)
except Exception as e:
print(f"Hardware encryption failed: {e}. Falling back to software.")
ciphertext = AES_128_CBC.encrypt(
plaintext=PKCS7.pad(data),
key=self._encryption_key,
iv=iv,
)
signed_parts = iv + ciphertext
try:
hmac = kryptor_hsm.hmac(self._signing_key, signed_parts)
except Exception as e:
print(f"Hardware HMAC failed: {e}. Falling back to software.")
hmac = HMAC.new(self._signing_key, signed_parts).digest()
return signed_parts + hmac
def decrypt(self, token=None):
if not isinstance(token, bytes):
raise TypeError("Token must be bytes")
if not self.verify_hmac(token):
raise ValueError("Token HMAC was invalid")
iv = token[:16]
ciphertext = token[16:-32]
try:
try:
plaintext = PKCS7.unpad(
kryptor_hsm.camellia_decrypt(
ciphertext,
self._encryption_key,
iv,
)
)
except Exception as e:
print(f"Hardware decryption failed: {e}. Falling back to software.")
plaintext = PKCS7.unpad(
AES_128_CBC.decrypt(
ciphertext,
self._encryption_key,
iv,
)
)
return plaintext
except Exception as e:
raise ValueError("Could not decrypt token")