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
|
# -*- coding: utf-8 -*-
#
# Cipher/DES3.py : DES3
#
# ===================================================================
# The contents of this file are dedicated to the public domain. To
# the extent that dedication to the public domain is not available,
# everyone is granted a worldwide, perpetual, royalty-free,
# non-exclusive license to exercise all rights associated with the
# contents of this file for any purpose whatsoever.
# No rights are reserved.
#
# 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.
# ===================================================================
"""Triple DES symmetric cipher
`Triple DES`__ (or TDES or TDEA or 3DES) is a symmetric block cipher standardized by NIST_.
It has a fixed data block size of 8 bytes. Its keys are 128 (*Option 1*) or 192
bits (*Option 2*) long.
However, 1 out of 8 bits is used for redundancy and do not contribute to
security. The effective key length is respectively 112 or 168 bits.
TDES consists of the concatenation of 3 simple `DES` ciphers.
The plaintext is first DES encrypted with *K1*, then decrypted with *K2*,
and finally encrypted again with *K3*. The ciphertext is decrypted in the reverse manner.
The 192 bit key is a bundle of three 64 bit independent subkeys: *K1*, *K2*, and *K3*.
The 128 bit key is split into *K1* and *K2*, whereas *K1=K3*.
It is important that all subkeys are different, otherwise TDES would degrade to
single `DES`.
TDES is cryptographically secure, even though it is neither as secure nor as fast
as `AES`.
As an example, encryption can be done as follows:
>>> from Crypto.Cipher import DES
>>> from Crypto import Random
>>> from Crypto.Util import Counter
>>>
>>> key = b'-8B key-'
>>> nonce = Random.new().read(DES.block_size/2)
>>> ctr = Counter.new(DES.block_size*8/2, prefix=nonce)
>>> cipher = DES.new(key, DES.MODE_CTR, counter=ctr)
>>> plaintext = b'We are no longer the knights who say ni!'
>>> msg = nonce + cipher.encrypt(plaintext)
.. __: http://en.wikipedia.org/wiki/Triple_DES
.. _NIST: http://csrc.nist.gov/publications/nistpubs/800-67/SP800-67.pdf
:undocumented: __revision__, __package__
"""
__revision__ = "$Id$"
from Crypto.Cipher import blockalgo
from Crypto.Cipher import _DES3
class DES3Cipher(blockalgo.BlockAlgo):
"""TDES cipher object"""
def __init__(self, key, *args, **kwargs):
"""Initialize a TDES cipher object
See also `new()` at the module level."""
blockalgo.BlockAlgo.__init__(self, _DES3, key, *args, **kwargs)
def new(key, *args, **kwargs):
"""Create a new TDES cipher
:Parameters:
key : byte string
The secret key to use in the symmetric cipher.
It must be 16 or 24 bytes long. The parity bits will be ignored.
:Keywords:
mode : a *MODE_** constant
The chaining mode to use for encryption or decryption.
Default is `MODE_ECB`.
IV : byte string
The initialization vector to use for encryption or decryption.
It is ignored for `MODE_ECB` and `MODE_CTR`.
For `MODE_OPENPGP`, IV must be `block_size` bytes long for encryption
and `block_size` +2 bytes for decryption (in the latter case, it is
actually the *encrypted* IV which was prefixed to the ciphertext).
It is mandatory.
For all other modes, it must be `block_size` bytes longs. It is optional and
when not present it will be given a default value of all zeroes.
counter : callable
(*Only* `MODE_CTR`). A stateful function that returns the next
*counter block*, which is a byte string of `block_size` bytes.
For better performance, use `Crypto.Util.Counter`.
segment_size : integer
(*Only* `MODE_CFB`).The number of bits the plaintext and ciphertext
are segmented in.
It must be a multiple of 8. If 0 or not specified, it will be assumed to be 8.
:Attention: it is important that all 8 byte subkeys are different,
otherwise TDES would degrade to single `DES`.
:Return: an `DES3Cipher` object
"""
return DES3Cipher(key, *args, **kwargs)
#: Electronic Code Book (ECB). See `blockalgo.MODE_ECB`.
MODE_ECB = 1
#: Cipher-Block Chaining (CBC). See `blockalgo.MODE_CBC`.
MODE_CBC = 2
#: Cipher FeedBack (CFB). See `blockalgo.MODE_CFB`.
MODE_CFB = 3
#: This mode should not be used.
MODE_PGP = 4
#: Output FeedBack (OFB). See `blockalgo.MODE_OFB`.
MODE_OFB = 5
#: CounTer Mode (CTR). See `blockalgo.MODE_CTR`.
MODE_CTR = 6
#: OpenPGP Mode. See `blockalgo.MODE_OPENPGP`.
MODE_OPENPGP = 7
#: Size of a data block (in bytes)
block_size = 8
#: Size of a key (in bytes)
key_size = ( 16, 24 )
|