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# Copyright © 2017 Tom Hacohen
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License as
# published by the Free Software Foundation, version 3.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import serialization, hashes, padding
from cryptography.hazmat.primitives.asymmetric import rsa, padding as asym_padding
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
import os
import hashlib
import hmac
try:
from hashlib import scrypt
def derive_key(user_password, salt):
return scrypt(password=user_password.encode(),
salt=salt.encode(),
n=16384,
r=8,
p=1,
dklen=190)
except ImportError:
try:
import scrypt
def derive_key(user_password, salt):
return scrypt.hash(password=user_password.encode(),
salt=salt.encode(),
N=16384,
r=8,
p=1,
buflen=190)
except ImportError:
import pyscrypt
def derive_key(user_password, salt):
return pyscrypt.hash(password=user_password.encode(),
salt=salt.encode(),
N=16384,
r=8,
p=1,
dkLen=190)
from . import exceptions
CURRENT_VERSION = 2
HMAC_SIZE = int(256 / 8) # 256bits in bytes
AES_BLOCK_SIZE = int(128 / 8) # 128bits in bytes
def hmac256(key, data):
return hmac.new(key, data, digestmod=hashlib.sha256).digest()
class AsymmetricKeyPair:
def __init__(self, private_key, public_key):
self.private_key = private_key
self.public_key = public_key
class AsymmetricCryptoManager:
def __init__(self, key_pair):
self.key_pair = key_pair
self._padding = asym_padding.OAEP(
mgf=asym_padding.MGF1(algorithm=hashes.SHA1()),
algorithm=hashes.SHA1(),
label=None
)
@classmethod
def generate_key_pair(cls):
private_key = rsa.generate_private_key(
public_exponent=65537,
key_size=3072,
backend=default_backend()
)
return AsymmetricKeyPair(
private_key.private_bytes(encryption_algorithm=serialization.NoEncryption(),
encoding=serialization.Encoding.DER,
format=serialization.PrivateFormat.PKCS8),
private_key.public_key().public_bytes(encoding=serialization.Encoding.DER,
format=serialization.PublicFormat.SubjectPublicKeyInfo))
def decrypt(self, ctext):
private_key = serialization.load_der_private_key(
self.key_pair.private_key, password=None, backend=default_backend())
return private_key.decrypt(
ctext,
self._padding
)
def encrypt(self, public_key, clear_text):
public_key = serialization.load_der_public_key(
self.key_pair.public_key, backend=default_backend())
return public_key.encrypt(
clear_text,
self._padding
)
class CryptoManager:
def __init__(self, version, key, salt):
if version > CURRENT_VERSION:
raise exceptions.VersionTooNew("Found version is too new. Found: {} Current: {}".format(
version, CURRENT_VERSION))
elif version == 1:
pass
else:
key = hmac256(salt, key)
self.version = version
self._set_derived_key(key)
@classmethod
def create_from_asymmetric_encryted_key(cls, version, key_pair, encrypted_key):
asymmetric_crypto_manager = AsymmetricCryptoManager(key_pair)
derived_key = asymmetric_crypto_manager.decrypt(encrypted_key)
ret = CryptoManager(version, b'', b'')
ret._set_derived_key(derived_key)
return ret
def _set_derived_key(self, key):
self.cipher_key = hmac256(b'aes', key)
self.hmacKey = hmac256(b'hmac', key)
def decrypt(self, ctext):
iv = ctext[:AES_BLOCK_SIZE]
ctext = ctext[AES_BLOCK_SIZE:]
cipher = Cipher(algorithms.AES(self.cipher_key), modes.CBC(iv), backend=default_backend())
unpadder = padding.PKCS7(AES_BLOCK_SIZE * 8).unpadder()
decryptor = cipher.decryptor()
data = decryptor.update(ctext) + decryptor.finalize()
return unpadder.update(data) + unpadder.finalize()
def encrypt(self, clear_text):
iv = os.urandom(AES_BLOCK_SIZE)
cipher = Cipher(algorithms.AES(self.cipher_key), modes.CBC(iv), backend=default_backend())
padder = padding.PKCS7(AES_BLOCK_SIZE * 8).padder()
encryptor = cipher.encryptor()
padded_data = padder.update(clear_text) + padder.finalize()
return iv + encryptor.update(padded_data) + encryptor.finalize()
def hmac(self, data):
if self.version == 1:
return hmac256(self.hmacKey, data)
else:
return hmac256(self.hmacKey, data + bytes([self.version]))
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