Reticulum/RNS/Cryptography/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
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import time
from RNS.Cryptography import HMAC
from RNS.Cryptography import PKCS7
from RNS.Cryptography.AES import AES_128_CBC
class Fernet():
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FERNET_VERSION = 0x80
FERNET_OVERHEAD = 57 # In bytes
OPTIMISED_FERNET_OVERHEAD = 54 # In bytes
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@staticmethod
def generate_key():
return os.urandom(32)
def __init__(self, key = None):
if key == None:
raise ValueError("Fernet key cannot be None")
if len(key) != 32:
raise ValueError("Fernet key must be 32 bytes, not "+str(len(key)))
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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 = HMAC.new(self._signing_key, token[:-32]).digest()
if received_hmac == expected_hmac:
return True
else:
return False
def encrypt(self, data = None):
iv = os.urandom(16)
current_time = int(time.time())
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if not isinstance(data, bytes):
raise TypeError("Fernet token plaintext input must be bytes")
ciphertext = AES_128_CBC.encrypt(
plaintext = PKCS7.pad(data),
key = self._encryption_key,
iv = iv,
)
signed_parts = b"\x80"+current_time.to_bytes(length=8, byteorder="big")+iv+ciphertext
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return signed_parts + HMAC.new(self._signing_key, signed_parts).digest()
def decrypt(self, token = None):
if not isinstance(token, bytes):
raise TypeError("Fernet token must be bytes")
if not self.verify_hmac(token):
raise ValueError("Fernet token HMAC was invalid")
iv = token[9:25]
ciphertext = token[25:-32]
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try:
plaintext = PKCS7.unpad(
AES_128_CBC.decrypt(
ciphertext,
self._encryption_key,
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iv,
)
)
return plaintext
except Exception as e:
raise ValueError("Could not decrypt Fernet token")