124 lines
4.5 KiB
Python
124 lines
4.5 KiB
Python
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# -*- coding: utf-8 -*-
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#
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# Cipher/CAST.py : CAST
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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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"""CAST-128 symmetric cipher
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CAST-128_ (or CAST5) is a symmetric block cipher specified in RFC2144_.
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It has a fixed data block size of 8 bytes. Its key can vary in length
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from 40 to 128 bits.
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CAST is deemed to be cryptographically secure, but its usage is not widespread.
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Keys of sufficient length should be used to prevent brute force attacks
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(128 bits are recommended).
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As an example, encryption can be done as follows:
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>>> from Crypto.Cipher import CAST
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>>> from Crypto import Random
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>>>
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>>> key = b'Sixteen byte key'
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>>> iv = Random.new().read(CAST.block_size)
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>>> cipher = CAST.new(key, CAST.MODE_OPENPGP, iv)
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>>> plaintext = b'sona si latine loqueris '
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>>> msg = cipher.encrypt(plaintext)
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>>>
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...
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>>> eiv = msg[:CAST.block_size+2]
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>>> ciphertext = msg[CAST.block_size+2:]
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>>> cipher = CAST.new(key, CAST.MODE_OPENPGP, eiv)
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>>> print cipher.decrypt(ciphertext)
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.. _CAST-128: http://en.wikipedia.org/wiki/CAST-128
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.. _RFC2144: http://tools.ietf.org/html/rfc2144
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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 _CAST
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class CAST128Cipher(blockalgo.BlockAlgo):
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"""CAST-128 cipher object"""
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def __init__(self, key, *args, **kwargs):
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"""Initialize a CAST-128 cipher object
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See also `new()` at the module level."""
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blockalgo.BlockAlgo.__init__(self, _CAST, key, *args, **kwargs)
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def new(key, *args, **kwargs):
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"""Create a new CAST-128 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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Its length may vary from 5 to 16 bytes.
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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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:Return: an `CAST128Cipher` object
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"""
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return CAST128Cipher(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 = range(5,16+1)
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