DES (Data Encryption Standard)

A pure Python implementation for the famous DES algorithm, supporting Python 2 and 3.

Installation

Using pip:

$ pip install des 

Or manually download the archive and run the command after extracting the stuff inside:

$ python setup.py install

Usage

Firstly, define a DesKey object by passing your encryption / decryption key. The key should be of length 8, 16 or 24. The algorithm will be automatically chosen for you. Note that the key should be written as bytes in Python 3.

from des import DesKey
key0 = DesKey(b"some key")                  # for DES
key1 = DesKey(b"a key for TRIPLE")          # for 3DES, same as "a key for TRIPLEa key fo"
key2 = DesKey(b"a 24-byte key for TRIPLE")  # for 3DES
key3 = DesKey(b"1234567812345678REAL_KEY")  # for DES, same as "REAL_KEY"

You may know whether a key is for DES or 3DES algorithm by calling its method is_single() or is_triple().

key0.is_single()  # -> True
key1.is_triple()  # -> True
key2.is_single()  # -> False
key3.is_triple()  # -> False

Secondly, encrypt messages by calling the method encrypt() from the DesKey object, or decrypt them by calling decrypt(). Note that the messages should be written as bytes in Python 3.

key0.encrypt(b"any long message")  # -> b"\x14\xfa\xc2 '\x00{\xa9\xdc;\x9dq\xcbr\x87Q"

By default, ECB Mode is used. You may enable CBC Mode by passing the argument initial, as the Initial Value. The argument may be either a bytes object of length 8 or an integer using big-endian.

key0.encrypt(b"any long message", initial=0)        # -> b"\x14\xfa\xc2 '\x00{\xa9\xb2\xa5\xa7\xfb#\x86\xc5\x9b"
key0.encrypt(b"any long message", initial=b"\0"*8)  # same as above

The DES algorithm requires the message to be of any length that is a multiple of 8. By default, the length of the message to encrypt / decrypt is assured by users. You may choose to turn on PKCS5 Padding Mode(by passing the argument padding with a TRUTHY value), telling Python to do the padding before encryption for you.

key0.encrypt(b"abc", padding=True)  # -> b"%\xd1KU\x8b_A\xa6"

While in decryption with PKCS5 Padding, the length of the message is still required to be a multiple of 8. But after decryption, Python will throw the padding characters away.

key0.decrypt(b"%\xd1KU\x8b_A\xa6", padding=True)  # -> b"abc"

Note

Because DES keys are 56 bits and the input key to this algorithm is 8, 16 or 24 bytes, this implementation ignores the least significant bit of each key byte.