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
|
# encryption.py - module for handling encrypted values
# coding: utf-8
#
# Copyright (C) 2014 Arthur de Jong
#
# This library 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; either
# version 2.1 of the License, or (at your option) any later version.
#
# 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
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
# 02110-1301 USA
"""Module that handles encrypted PSKC values.
This module defines an Encryption class that handles the encryption key
and an EncryptedValue wrapper class that can decrypt values using the
encryption key.
The encryption key can be derived using the KeyDerivation class.
"""
import base64
from Crypto.Cipher import AES
from Crypto.Protocol.KDF import PBKDF2
AES128_CBC = 'http://www.w3.org/2001/04/xmlenc#aes128-cbc'
class EncryptedValue(object):
"""Wrapper class to handle encrypted values.
Instances of this class provide the following attributes:
algorithm: name of the encryption algorithm used
cipher_value: binary encrypted data
"""
def __init__(self, encryption, encrypted_value=None):
"""Initialise an encrypted value for the provided Key."""
self.encryption = encryption
self.algorithm = None
self.cipher_value = None
self.parse(encrypted_value)
def parse(self, encrypted_value):
"""Read encrypted data from the <EncryptedValue> XML tree."""
from pskc.parse import g_e_v, namespaces
if encrypted_value is None:
return
encryption_method = encrypted_value.find(
'xenc:EncryptionMethod', namespaces=namespaces)
self.algorithm = encryption_method.attrib.get('Algorithm')
value = g_e_v(encrypted_value, 'xenc:CipherData/xenc:CipherValue')
if value is not None:
self.cipher_value = base64.b64decode(value)
def decrypt(self):
"""Decrypt the linked value and return the plaintext value."""
key = self.encryption.key
ciphertext = self.cipher_value
if key is None or ciphertext is None:
return
if self.algorithm == AES128_CBC:
iv = ciphertext[:AES.block_size]
cipher = AES.new(key, AES.MODE_CBC, iv)
plaintext = cipher.decrypt(ciphertext[AES.block_size:])
return plaintext[0:-ord(plaintext[-1])]
PBKDF2_URIS = [
'http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5#pbkdf2',
'http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5v2-0#pbkdf2',
'http://www.w3.org/2009/xmlenc11#pbkdf2',
]
class KeyDerivation(object):
"""Handle key derivation.
The algorithm property contains the key derivation algorithm to use. For
PBDKF2 the following parameters are set:
pbkdf2_salt: salt value
pbkdf2_iterations: number of iterations to use
pbkdf2_key_length: required key lengt
pbkdf2_prf: name of pseudorandom function used (HMAC-SHA1 is assumed)
"""
def __init__(self, key_deriviation=None):
self.algorithm = None
# PBKDF2 properties
self.pbkdf2_salt = None
self.pbkdf2_iterations = None
self.pbkdf2_key_length = None
self.pbkdf2_prf = None
self.parse(key_deriviation)
def parse(self, key_deriviation):
"""Read derivation parameters from a <KeyDerivationMethod> element."""
from pskc.parse import g_e_v, g_e_i, namespaces
if key_deriviation is None:
return
self.algorithm = key_deriviation.attrib.get('Algorithm')
# PBKDF2 properties
pbkdf2 = key_deriviation.find(
'xenc11:PBKDF2-params', namespaces=namespaces)
if pbkdf2 is None:
pbkdf2 = key_deriviation.find(
'pkcs5:PBKDF2-params', namespaces=namespaces)
if pbkdf2 is not None:
# get used salt
value = g_e_v(pbkdf2, 'Salt/Specified')
if value is not None:
self.pbkdf2_salt = base64.b64decode(value)
# required number of iterations
self.pbkdf2_iterations = g_e_i(pbkdf2, 'IterationCount')
# key length
self.pbkdf2_key_length = g_e_i(pbkdf2, 'KeyLength')
# pseudorandom function used
prf = pbkdf2.find('PRF', namespaces=namespaces)
if prf is not None:
self.pbkdf2_prf = prf.attrib.get('Algorithm')
def generate(self, password):
"""Derive a key from the password."""
if self.algorithm in PBKDF2_URIS:
# TODO: support pseudorandom function (prf)
return PBKDF2(
password, self.pbkdf2_salt, dkLen=self.pbkdf2_key_length,
count=self.pbkdf2_iterations, prf=None)
class Encryption(object):
"""Class for handling encryption keys that are used in the PSKC file.
Encryption generally uses a symmetric key that is used to encrypt some
of the information stored in PSKC files (typically the seed). This
class provides the following values:
id: identifier of the key
key_names: list of names for the key
key_name: (first) name of the key (usually there is only one)
key: the key value itself (binary form)
The key can either be included in the PSKC file (in that case it
automatically picked up) or derived using the derive_key() method.
"""
def __init__(self, key_info=None):
self.id = None
self.key_names = []
self.key = None
self.derivation = KeyDerivation()
self.parse(key_info)
def parse(self, key_info):
"""Read encryption information from the <EncryptionKey> XML tree."""
from pskc.parse import g_e_v, namespaces
if key_info is None:
return
self.id = key_info.attrib.get('Id')
for name in key_info.findall('ds:KeyName', namespaces=namespaces):
self.key_names.append(g_e_v(name, '.'))
for name in key_info.findall(
'xenc11:DerivedKey/xenc11:MasterKeyName',
namespaces=namespaces):
self.key_names.append(g_e_v(name, '.'))
self.derivation.parse(key_info.find(
'xenc11:DerivedKey/xenc11:KeyDerivationMethod',
namespaces=namespaces))
@property
def key_name(self):
"""Provide the name of the (first) key."""
if self.key_names:
return self.key_names[0]
def derive_key(self, password):
"""Derive a key from the password."""
self.key = self.derivation.generate(password)
|