Current File : //opt/alt/python37/lib64/python3.7/site-packages/Crypto/Cipher/DES.py
# -*- coding: utf-8 -*-
#
# Cipher/DES.py : DES
#
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# the extent that dedication to the public domain is not available,
# everyone is granted a worldwide, perpetual, royalty-free,
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# No rights are reserved.
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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"""DES symmetric cipher
DES `(Data Encryption Standard)`__ is a symmetric block cipher standardized
by NIST_ . It has a fixed data block size of 8 bytes.
Its keys are 64 bits long, even though 8 bits were used for integrity (now they
are ignored) and do not contribute to securty.
DES is cryptographically secure, but its key length is too short by nowadays
standards and it could be brute forced with some effort.
DES should not be used for new designs. Use `AES`.
As an example, encryption can be done as follows:
>>> from Crypto.Cipher import DES3
>>> from Crypto import Random
>>>
>>> key = b'Sixteen byte key'
>>> iv = Random.new().read(DES3.block_size)
>>> cipher = DES3.new(key, DES3.MODE_OFB, iv)
>>> plaintext = b'sona si latine loqueris '
>>> msg = iv + cipher.encrypt(plaintext)
.. __: http://en.wikipedia.org/wiki/Data_Encryption_Standard
.. _NIST: http://csrc.nist.gov/publications/fips/fips46-3/fips46-3.pdf
:undocumented: __revision__, __package__
"""
__revision__ = "$Id$"
from Crypto.Cipher import blockalgo
from Crypto.Cipher import _DES
class DESCipher(blockalgo.BlockAlgo):
"""DES cipher object"""
def __init__(self, key, *args, **kwargs):
"""Initialize a DES cipher object
See also `new()` at the module level."""
blockalgo.BlockAlgo.__init__(self, _DES, key, *args, **kwargs)
def new(key, *args, **kwargs):
"""Create a new DES cipher
:Parameters:
key : byte string
The secret key to use in the symmetric cipher.
It must be 8 byte 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.
:Return: an `DESCipher` object
"""
return DESCipher(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 = 8
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