exclusive

Data structure for representing secret shares of byte vectors based on bitwise XOR, designed for use within secure multi-party computation (MPC) protocol implementations.

Purpose

This library provides a data structure and methods that make it possible to work with n-out-of-n XOR-based secret shares of bytes-like objects within secure multi-party computation (MPC) protocol implementations. Secret shares are represented using instances of class derived from bytes, and functions are provided both for splitting bytes-like objects into shares and for reconstructing bytes objects from shares.

Installation and Usage

This library is available as a package on PyPI:

python -m pip install exclusive

The library can be imported in the usual ways:

import exclusive
from exclusive import *

Examples

This library makes it possible to concisely construct multiple XOR-based secret shares from a bytes-like object:

>>> from exclusive import shares, xor
>>> (a, b) = shares(bytes([1, 2, 3]))
>>> (c, d) = shares(bytes([4, 5, 6]))
>>> ((a ^ c) ^ (b ^ d)) == xor([bytes([1, 2, 3]), bytes([4, 5, 6])])
True

The number of shares can be specified explicitly (the default is two shares):

>>> (r, s, t) = shares(bytes([1, 2, 3]), quantity=3)

For convenience, an xor operator that is analogous to Python's built-in sum function is provided:

>>> xor([bytes([1, 2, 3]), bytes([4, 5, 6])]).hex()
'050705

The share class is derived from the bytes class. Thus, all methods, operators, and functions that operate on bytes-like objects are supported for share objects. The xor operator provided by the library relies on Python's built-in exclusive or operator and can be used for concise reconstruction of values from a collection of secret shares:

>>> xor([r, s, t]) == bytes([1, 2, 3])
True

In addition, conversion methods for Base64 strings are included to support encoding and decoding of share objects:

>>> share.from_base64('HgEA').hex()
'1e0100'
>>> [s.to_base64() for s in shares(bytes([1, 2, 3]))]
['mB6G', 'mRyF']

Development

All installation and development dependencies are fully specified in pyproject.toml. The project.optional-dependencies object is used to specify optional requirements for various development tasks. This makes it possible to specify additional options (such as docs, lint, and so on) when performing installation using pip:

python -m pip install .[docs,lint]

Documentation

The documentation can be generated automatically from the source files using Sphinx:

python -m pip install .[docs]
cd docs
sphinx-apidoc -f -E --templatedir=_templates -o _source .. && make html

Testing and Conventions

All unit tests are executed and their coverage is measured when using pytest (see the pyproject.toml file for configuration details):

python -m pip install .[test]
python -m pytest

Alternatively, all unit tests are included in the module itself and can be executed using doctest:

python src/exclusive/exclusive.py -v

Style conventions are enforced using Pylint:

python -m pip install .[lint]
python -m pylint src/exclusive

Contributions

In order to contribute to the source code, open an issue or submit a pull request on the GitHub page for this library.

Versioning

The version number format for this library and the changes to the library associated with version number increments conform with Semantic Versioning 2.0.0.

Publishing

This library can be published as a package on PyPI by a package maintainer. First, install the dependencies required for packaging and publishing:

python -m pip install .[publish]

Ensure that the correct version number appears in pyproject.toml, and that any links in this README document to the Read the Docs documentation of this package (or its dependencies) have appropriate version numbers. Also ensure that the Read the Docs project for this library has an automation rule that activates and sets as the default all tagged versions. Create and push a tag for this version (replacing ?.?.? with the version number):

git tag ?.?.?
git push origin ?.?.?

Remove any old build/distribution files. Then, package the source into a distribution archive:

rm -rf build dist src/*.egg-info
python -m build --sdist --wheel .

Finally, upload the package distribution archive to PyPI:

python -m twine upload dist/*