Python-LowMC

Description

Python-LowMC is a Python reimplementation of the LowMC blockcipher. LowMC is used in the Post-quantum signature scheme Picnic. Python-LowMC exists because i want to understand and learn the Picnic algorithm. Therefore i started with LowMC as one part of Picnic. There is a own Github repo Python-Picnic for the Python implementation of Picnic.

References

LowMC (Low Multiplicative Complexity) is a blockcipher. The reference implementation is in C++ under MIT licence and can be found here:

LowMC Github

The LowMC paper is available at:

LowMC paper

The files in this Repository (Python-LowMC) are a Python re-implementation of LowMC for usage with the Picnic Post-quantum signature algorithm. The Picnic reference implementation is in C under MIT license and can be found here:

Picnic Github

The Picnic paper is available at:

Picnic paper

Disclaimer

This implementation is for the sole purpose of learning and understanding the LowMC algorithm. It's not recommended to use this code in productive environment. Additionaly this code is very slow, compared to the reference implementation (in C++). LowMC is optimized for efficient implementation in hardware, not in high-level languages like Python.

Prerequisites

Python3 (tested with 3.6)
Additional package: BitVector

It's recommended to use a Python virtual environment like virtualenv. The BitVector package can be installed with

pip install BitVector

Usage

Constants and matrices

LowMC needs pre-calculated constants and matrices. Therefore the python-file generator.py is included. The generator creates picnic-<x>.dat files with <x> beeing the security level L1, L2 or L3. There are three pre-calculated files contained in this repository. They can be used for the tests without generating them.

If you wish to generate them for yourself, execute

generator.py <arg>

with <arg> beeing one of the parameters picnic-L1, picnic-L2 or picnic-L3. For the detailed parameter sets of each security level see the Picnic paper (Link above).

Tests

To run the tests with the Picnic-testvectors, simply execute `` test_lowmc.py `` There are 9 testvectors included. Three for each security level. They are taken from the Picnic reference implementation (Link above).

The LowMC Class

You can instantiate LowMC by creating a LowMC Object from the file lowmc.py with the security level as a parameter string:

lowmc = LowMC('picnic-<x>')

with <x> beeing the security level L1, L2 or L3.

On the LowMC object the following public functions are available:

lowmc.generate_priv_key()
lowmc.set_priv_key(priv_key)
lowmc.encrypt(plaintext)
lowmc.decrypt(ciphertext)

Where the parameters priv_key, plaintext and ciphertext are raw bytes and their lengths have to match the security level parameters for keysize and blocksize.

For examples see the file test_lowmc.py.

Note

This project has been set up using PyScaffold 3.1. For details and usage information on PyScaffold see https://pyscaffold.org/.

ThorKn/Python-LowMC