131 lines
4.3 KiB
Markdown
131 lines
4.3 KiB
Markdown
# About
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Author: Todd Whiteman
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Version: 2.0.1
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Release: 28th April, 2010
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License: MIT
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This is a pure python implementation of the DES encryption algorithm.
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It's pure python to avoid portability issues, since most DES
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implementations are programmed in C (for performance reasons).
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## Installation
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Using the Python package manager:
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```bash
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$ pip install pydes
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```
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### Or, for manual installation
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Extract the files from the downloaded archive and run:
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```
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$ python setup.py install
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```
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If you'd like to run the tests, run the command:
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```
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$ python test_pydes.py
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```
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## Usage
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```bash
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python -c "import pyDes; des = pyDes.des('This Key'); \
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print des.encrypt('SomeData').encode('hex')"
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```
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### Docs and Examples
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```
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Class initialization
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--------------------
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pyDes.des(key, [mode], [IV], [pad], [padmode])
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pyDes.triple_des(key, [mode], [IV], [pad], [padmode])
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key -> Bytes containing the encryption key. 8 bytes for DES, 16 or 24 bytes
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for Triple DES
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mode -> Optional argument for encryption type, can be either
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pyDes.ECB (Electronic Code Book) or pyDes.CBC (Cypher Block Chaining)
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IV -> Optional Initial Value bytes, must be supplied if using CBC mode.
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Length must be 8 bytes.
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pad -> Optional argument, set the pad character (PAD_NORMAL) to use during
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all encrypt/decrpt operations done with this instance.
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padmode -> Optional argument, set the padding mode (PAD_NORMAL or PAD_PKCS5)
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to use during all encrypt/decrypt operations done with this instance.
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I recommend to use PAD_PKCS5 padding, as then you never need to worry about any
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padding issues, as the padding can be removed unambiguously upon decrypting
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data that was encrypted using PAD_PKCS5 padmode.
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Common methods
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--------------
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encrypt(data, [pad], [padmode])
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decrypt(data, [pad], [padmode])
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data -> Bytes to be encrypted/decrypted
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pad -> Optional argument. Only when using padmode of PAD_NORMAL. For
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encryption, adds this characters to the end of the data block when
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data is not a multiple of 8 bytes. For decryption, will remove the
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trailing characters that match this pad character from the last 8
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bytes of the unencrypted data block.
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padmode -> Optional argument, set the padding mode, must be one of PAD_NORMAL
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or PAD_PKCS5). Defaults to PAD_NORMAL.
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Example
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-------
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import pyDes
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# For Python3, you'll need to use bytes, i.e.:
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# data = b"Please encrypt my data"
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# k = pyDes.des(b"DESCRYPT", pyDes.CBC, b"\0\0\0\0\0\0\0\0", pad=None, padmode=pyDes.PAD_PKCS5)
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data = "Please encrypt my data"
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k = pyDes.des("DESCRYPT", pyDes.CBC, "\0\0\0\0\0\0\0\0", pad=None, padmode=pyDes.PAD_PKCS5)
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d = k.encrypt(data)
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print "Encrypted: %r" % d
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print "Decrypted: %r" % k.decrypt(d)
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assert k.decrypt(d) == data
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See the pyDes test file (test_pydes.py) for more examples of use.
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Note: This code was not written for high-end systems needing a fast
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implementation, but rather a handy portable solution with small usage.
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```
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## Performance
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The code is not written for speed or performance, so not for those
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needing a fast DES implementation, but rather a handy portable solution ideal
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for small usages. The speed at which pyDes encrypts/decrypts is around 10Kb/s
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(using the DES method) - that's very SLOW!!
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## About triple DES
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Triple DES is just running the DES algorithm 3 times over the data with the
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specified key. The supplied key is split up into 3 parts, each part being 8
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bytes long (the mandatory key size for DES).
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The triple DES algorithm uses the DES-EDE3 method when a 24 byte key is
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supplied. This means there are three DES operations in the sequence
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encrypt-decrypt-encrypt with the three different keys. The first key will be
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bytes 1 to 8, the second key bytes 9 to 16 and the third key bytes 17 to 24.
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If a 16 byte key is supplied instead, the triple DES method used will be
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DES-EDE2. This means there are three DES operations in the sequence
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encrypt-decrypt-encrypt, but the first and third operations use the same key.
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The first/third key will be bytes 1 to 8 and the second key bytes 9 to 16.
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## Credits
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Thanks go to:
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- David Broadwell: Ideas, comments and suggestions.
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- Mario Wolff: Finding and debugging triple des CBC errors.
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- Santiago Palladino: Providing the PKCS5 padding technique.
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- Shaya: Fixing triple DES CBC errors with PAD_PKCS5.
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- Yoav Aner: For spotting a triple DES CBC IV error.
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