SM4

A pure Python implementation for the famous SM4 algorithm, supporting Python 2 and 3.

Installation

Using pip:

$ pip install sm4 

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

$ python setup.py install

Usage

Firstly, define a SM4Key object by passing your encryption / decryption key. The key should be of length 16. Note that the key should be written as bytes in Python 3.

from sm4 import SM4Key
key0 = SM4Key(b"any length16 key")

Secondly, encrypt messages by calling the method encrypt() from the SM4Key object, or decrypt them by calling decrypt(). Note that the messages should be written as bytes in Python 3.

key0.encrypt(b"Any very very very long message!")  # -> b'\x15\x8a\x18_qg\xf4%\x080\xb2HEFFO\x90\x0e\xc1\xbb\x07\xe5\xae\xed\xd5\x90\xf4K\xfb\xae]\xae'

By default, ECB Mode is used. You may enable CBC Mode by passing the argument initial, as the Initial Value. The argument should be a bytes object of length 16.

key0.encrypt(b"any long message", initial=b"\0"*16)        # -> b'\x15\x8a\x18_qg\xf4%\x080\xb2HEFFO\x98\x01}1\xe3\xa5oL\xdf\x95(A\xd8\xce\x14\xc9'

The SM4 algorithm requires the message to be of any length that is a multiple of 16. 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'K\x9euZ\x03\x96\xe0\x93+\xc9%Z\xab\xf5\xff\x17'

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"K\x9euZ\x03\x96\xe0\x93+\xc9%Z\xab\xf5\xff\x17", padding=True)  # -> b"abc"