1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
|
# -*- coding: utf-8 -*-
# crypto.py
# Copyright (C) 2013 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/>.
"""
Cryptographic utilities for Soledad.
"""
import os
import binascii
import hmac
import hashlib
from Crypto.Cipher import AES
from Crypto.Util import Counter
from leap.common.check import leap_assert, leap_assert_type
class EncryptionMethods(object):
"""
Representation of encryption methods that can be used.
"""
AES_256_CTR = 'aes-256-ctr'
class UnknownEncryptionMethod(Exception):
"""
Raised when trying to encrypt/decrypt with unknown method.
"""
pass
class NoSymmetricSecret(Exception):
"""
Raised when trying to get a hashed passphrase.
"""
class SoledadCrypto(object):
"""
General cryptographic functionality.
"""
MAC_KEY_LENGTH = 64
def __init__(self, soledad):
"""
Initialize the crypto object.
@param soledad: A Soledad instance for key lookup.
@type soledad: leap.soledad.Soledad
"""
self._soledad = soledad
def encrypt_sym(self, data, key,
method=EncryptionMethods.AES_256_CTR):
"""
Encrypt C{data} using a {password}.
Currently, the only encryption method supported is AES-256 CTR mode.
@param data: The data to be encrypted.
@type data: str
@param key: The key used to encrypt C{data} (must be 256 bits long).
@type key: str
@param method: The encryption method to use.
@type method: str
@return: A tuple with the initial value and the encrypted data.
@rtype: (long, str)
"""
leap_assert_type(key, str)
# AES-256 in CTR mode
if method == EncryptionMethods.AES_256_CTR:
leap_assert(
len(key) == 32, # 32 x 8 = 256 bits.
'Wrong key size: %s bits (must be 256 bits long).' % (len(key)*8))
iv = os.urandom(8)
ctr = Counter.new(64, prefix=iv)
cipher = AES.new(key=key, mode=AES.MODE_CTR, counter=ctr)
return binascii.b2a_base64(iv), cipher.encrypt(data)
# raise if method is unknown
raise UnknownEncryptionMethod('Unkwnown method: %s' % method)
def decrypt_sym(self, data, key,
method=EncryptionMethods.AES_256_CTR, **kwargs):
"""
Decrypt data using symmetric secret.
Currently, the only encryption method supported is AES-256 CTR mode.
@param data: The data to be decrypted.
@type data: str
@param key: The key used to decrypt C{data} (must be 256 bits long).
@type key: str
@param method: The encryption method to use.
@type method: str
@param kwargs: Other parameters specific to each encryption method.
@type kwargs: dict
@return: The decrypted data.
@rtype: str
"""
leap_assert_type(key, str)
# AES-256 in CTR mode
if method == EncryptionMethods.AES_256_CTR:
# assert params
leap_assert(
len(key) == 32, # 32 x 8 = 256 bits.
'Wrong key size: %s (must be 256 bits long).' % len(key))
leap_assert(
'iv' in kwargs,
'AES-256-CTR needs an initial value given as.')
ctr = Counter.new(64, prefix=binascii.a2b_base64(kwargs['iv']))
cipher = AES.new(key=key, mode=AES.MODE_CTR, counter=ctr)
return cipher.decrypt(data)
# raise if method is unknown
raise UnknownEncryptionMethod('Unkwnown method: %s' % method)
def doc_passphrase(self, doc_id):
"""
Generate a passphrase for symmetric encryption of document's contents.
The password is derived using HMAC having sha256 as underlying hash
function. The key used for HMAC are the first
C{soledad.REMOTE_STORAGE_SECRET_KENGTH} bytes of Soledad's storage
secret stripped from the first MAC_KEY_LENGTH characters. The HMAC
message is C{doc_id}.
@param doc_id: The id of the document that will be encrypted using
this passphrase.
@type doc_id: str
@return: The passphrase.
@rtype: str
@raise NoSymmetricSecret: if no symmetric secret was supplied.
"""
if self.secret is None:
raise NoSymmetricSecret()
return hmac.new(
self.secret[
self.MAC_KEY_LENGTH:
self._soledad.REMOTE_STORAGE_SECRET_LENGTH],
doc_id,
hashlib.sha256).digest()
def doc_mac_key(self, doc_id):
"""
Generate a key for calculating a MAC for a document whose id is
C{doc_id}.
The key is derived using HMAC having sha256 as underlying hash
function. The key used for HMAC is the first MAC_KEY_LENGTH characters
of Soledad's storage secret. The HMAC message is C{doc_id}.
@param doc_id: The id of the document.
@type doc_id: str
@return: The key.
@rtype: str
@raise NoSymmetricSecret: if no symmetric secret was supplied.
"""
if self.secret is None:
raise NoSymmetricSecret()
return hmac.new(
self.secret[:self.MAC_KEY_LENGTH],
doc_id,
hashlib.sha256).digest()
#
# secret setters/getters
#
def _get_secret(self):
return self._soledad.storage_secret
secret = property(
_get_secret, doc='The secret used for symmetric encryption')
|
