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