131 lines
4.8 KiB
Python
131 lines
4.8 KiB
Python
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# -*- coding: utf-8 -*-
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#
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# Cipher/ARC2.py : ARC2.py
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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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"""RC2 symmetric cipher
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RC2_ (Rivest's Cipher version 2) is a symmetric block cipher designed
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by Ron Rivest in 1987. The cipher started as a proprietary design,
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that was reverse engineered and anonymously posted on Usenet in 1996.
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For this reason, the algorithm was first called *Alleged* RC2 (ARC2),
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since the company that owned RC2 (RSA Data Inc.) did not confirm whether
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the details leaked into public domain were really correct.
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The company eventually published its full specification in RFC2268_.
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RC2 has a fixed data block size of 8 bytes. Length of its keys can vary from
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8 to 128 bits. One particular property of RC2 is that the actual
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cryptographic strength of the key (*effective key length*) can be reduced
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via a parameter.
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Even though RC2 is not cryptographically broken, it has not been analyzed as
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thoroughly as AES, which is also faster than RC2.
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New designs should not use RC2.
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As an example, encryption can be done as follows:
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>>> from Crypto.Cipher import ARC2
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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(ARC2.block_size)
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>>> cipher = ARC2.new(key, ARC2.MODE_CFB, iv)
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>>> msg = iv + cipher.encrypt(b'Attack at dawn')
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.. _RC2: http://en.wikipedia.org/wiki/RC2
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.. _RFC2268: http://tools.ietf.org/html/rfc2268
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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 _ARC2
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class RC2Cipher (blockalgo.BlockAlgo):
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"""RC2 cipher object"""
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def __init__(self, key, *args, **kwargs):
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"""Initialize an ARC2 cipher object
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See also `new()` at the module level."""
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blockalgo.BlockAlgo.__init__(self, _ARC2, key, *args, **kwargs)
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def new(key, *args, **kwargs):
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"""Create a new RC2 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 can vary from 1 to 128 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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effective_keylen : integer
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Maximum cryptographic strength of the key, in bits.
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It can vary from 0 to 1024. The default value is 1024.
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:Return: an `RC2Cipher` object
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"""
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return RC2Cipher(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(1,16+1)
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