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# -*- coding: utf-8 -*-
# _secrets/crypto.py
# Copyright (C) 2016 LEAP
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program 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/>.
import binascii
import json
import os
import scrypt
from leap.soledad.common import soledad_assert
from leap.soledad.common.log import getLogger
from leap.soledad.client._crypto import encrypt_sym, decrypt_sym, ENC_METHOD
from leap.soledad.client._secrets.util import SecretsError
logger = getLogger(__name__)
class SecretsCrypto(object):
VERSION = 2
def __init__(self, soledad):
self._soledad = soledad
def _get_key(self, salt):
passphrase = self._soledad.passphrase.encode('utf8')
key = scrypt.hash(passphrase, salt, buflen=32)
return key
#
# encryption
#
def encrypt(self, secrets):
encoded = {}
for name, value in secrets.iteritems():
encoded[name] = binascii.b2a_base64(value)
plaintext = json.dumps(encoded)
salt = os.urandom(64) # TODO: get salt length from somewhere else
key = self._get_key(salt)
iv, ciphertext = encrypt_sym(plaintext, key,
method=ENC_METHOD.aes_256_gcm)
encrypted = {
'version': self.VERSION,
'kdf': 'scrypt',
'kdf_salt': binascii.b2a_base64(salt),
'kdf_length': len(key),
'cipher': ENC_METHOD.aes_256_gcm,
'length': len(plaintext),
'iv': str(iv),
'secrets': binascii.b2a_base64(ciphertext),
}
return encrypted
#
# decryption
#
def decrypt(self, data):
version = data.setdefault('version', 1)
method = getattr(self, '_decrypt_v%d' % version)
try:
return method(data)
except Exception as e:
logger.error('error decrypting secrets: %r' % e)
raise SecretsError(e)
def _decrypt_v1(self, data):
# get encrypted secret from dictionary: the old format allowed for
# storage of more than one secret, but this feature was never used and
# soledad has been using only one secret so far. As there is a corner
# case where the old 'active_secret' key might not be set, we just
# ignore it and pop the only secret found in the 'storage_secrets' key.
secret_id = data['storage_secrets'].keys().pop()
encrypted = data['storage_secrets'][secret_id]
# assert that we know how to decrypt the secret
soledad_assert('cipher' in encrypted)
cipher = encrypted['cipher']
if cipher == 'aes256':
cipher = ENC_METHOD.aes_256_ctr
soledad_assert(cipher in ENC_METHOD)
# decrypt
salt = binascii.a2b_base64(encrypted['kdf_salt'])
key = self._get_key(salt)
separator = ':'
iv, ciphertext = encrypted['secret'].split(separator, 1)
ciphertext = binascii.a2b_base64(ciphertext)
plaintext = self._decrypt(key, iv, ciphertext, encrypted, cipher)
# create secrets dictionary
secrets = {
'remote_secret': plaintext[0:512],
'local_salt': plaintext[512:576],
'local_secret': plaintext[576:1024],
}
return secrets
def _decrypt_v2(self, encrypted):
cipher = encrypted['cipher']
soledad_assert(cipher in ENC_METHOD)
salt = binascii.a2b_base64(encrypted['kdf_salt'])
key = self._get_key(salt)
iv = encrypted['iv']
ciphertext = binascii.a2b_base64(encrypted['secrets'])
plaintext = self._decrypt(
key, iv, ciphertext, encrypted, cipher)
encoded = json.loads(plaintext)
secrets = {}
for name, value in encoded.iteritems():
secrets[name] = binascii.a2b_base64(value)
return secrets
def _decrypt(self, key, iv, ciphertext, encrypted, method):
# assert some properties of the stored secret
soledad_assert(encrypted['kdf'] == 'scrypt')
soledad_assert(encrypted['kdf_length'] == len(key))
# decrypt
plaintext = decrypt_sym(ciphertext, key, iv, method)
soledad_assert(encrypted['length'] == len(plaintext))
return plaintext
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