pyDes

[KhiZaRix]

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Author: Todd Whiteman

Issue Date: 28th April, 2010

Version: 2.0.1

Compatibility: Requires Python 2.2 or higher, an older Python 1.5.2 compatible module can be found in the CVS source.

Download ( Unix/PC ) = http://twhiteman.netfirms.com/pyDES/pyDes-2.0.1.tar.gz / http://twhiteman.netfirms.com/pyDES/pyDes-2.0.1.zip

About pyDES

This is a pure python implementation of the DES encryption algorithm. It is in pure python to avoid portability issues, since most DES implementations are programmed in C (for performance reasons).

Triple DES class is also implemented, utilising the DES base. Triple DES is either DES-EDE3 with a 24 byte key, or DES-EDE2 with a 16 byte key. See the "About triple DES" section below more info on this algorithm.

The code below is not written for speed or performance, so not for those needing a fast des implementation, but rather a handy portable solution ideal for small usage. It takes my AMD2000+ machine 1 second per 2.5 kilobyte to encrypt or decrypt using the DES method. Thats very SLOW!!

About triple DES

Triple DES is just running the DES algorithm 3 times over the data with the specified key. The supplied key is split up into 3 parts, each part being 8 bytes long (the mandatory key size for DES).

The triple DES algorithm uses the DES-EDE3 method when a 24 byte key is supplied. This means there are three DES operations in the sequence encrypt-decrypt-encrypt with the three different keys. The first key will be bytes 1 to 8, the second key bytes 9 to 16 and the third key bytes 17 to 24.

If a 16 byte key is supplied instead, the triple DES method used will be DES-EDE2. This means there are three DES operations in the sequence encrypt-decrypt-encrypt, but the first and third operations use the same key. The first/third key will be bytes 1 to 8 and the second key bytes 9 to 16.

Installation

1 Extract the files from the pyDes archive.

2 Run the following command: python setup.py install

3 To test, run: python test_pydes.py

Note: On Unix, you'd run this command from a shell prompt; on Windows, you have to open a command prompt window (``DOS box'') and do it there;

pyDes Usage

Class initialization
--------------------
pyDes.des(key, [mode], [IV], [pad], [padmode])
pyDes.triple_des(key, [mode], [IV], [pad], [padmode])

key     -> Bytes containing the encryption key. 8 bytes for DES, 16 or 24 bytes
	   for Triple DES
mode    -> Optional argument for encryption type, can be either
	   pyDes.ECB (Electronic Code Book) or pyDes.CBC (Cypher Block Chaining)
IV      -> Optional Initial Value bytes, must be supplied if using CBC mode.
	   Length must be 8 bytes.
pad     -> Optional argument, set the pad character (PAD_NORMAL) to use during
	   all encrypt/decrpt operations done with this instance.
padmode -> Optional argument, set the padding mode (PAD_NORMAL or PAD_PKCS5)
	   to use during all encrypt/decrpt operations done with this instance.

I recommend to use PAD_PKCS5 padding, as then you never need to worry about any
padding issues, as the padding can be removed unambiguously upon decrypting
data that was encrypted using PAD_PKCS5 padmode.

Common methods
--------------
encrypt(data, [pad], [padmode])
decrypt(data, [pad], [padmode])

data    -> Bytes to be encrypted/decrypted
pad     -> Optional argument. Only when using padmode of PAD_NORMAL. For
	   encryption, adds this characters to the end of the data block when
	   data is not a multiple of 8 bytes. For decryption, will remove the
	   trailing characters that match this pad character from the last 8
	   bytes of the unencrypted data block.
padmode -> Optional argument, set the padding mode, must be one of PAD_NORMAL
	   or PAD_PKCS5). Defaults to PAD_NORMAL.


Example
-------
from pyDes import *

# For Python3, you'll need to use bytes, i.e.:
#   data = b"Please encrypt my data"
#   k = des(b"DESCRYPT", CBC, b"\0\0\0\0\0\0\0\0", pad=None, padmode=PAD_PKCS5)

data = "Please encrypt my data"
k = des("DESCRYPT", CBC, "\0\0\0\0\0\0\0\0", pad=None, padmode=PAD_PKCS5)
d = k.encrypt(data)
print "Encrypted: %r" % d
print "Decrypted: %r" % k.decrypt(d)
assert k.decrypt(d, padmode=PAD_PKCS5) == data

Sources : pyDes - Pure Python DES encryption algorithm / pyDES download | SourceForge.net

Credits

Thanks go to:
David Broadwell for his ideas, comments and suggestions.
Mario Wolff for finding errors in triple des CBC.
Santiago Palladino for enlightening me on the PKCS5 padding technique.
Shaya for correcting the PAD_PKCS5 triple des CBC errors.
Yoav Aner for spotting a triple des CBC IV error.Thanks go to:
David Broadwell for his ideas, comments and suggestions.
Mario Wolff for finding errors in triple des CBC.
Santiago Palladino for enlightening me on the PKCS5 padding technique.
Shaya for correcting the PAD_PKCS5 triple des CBC errors.
Yoav Aner for spotting a triple des CBC IV error.

Edited August 20, 2015 by KhiZaRix