NuBLS

NuBLS is NuCypher's BLS signature library that implements threshold protocols like threshold signatures and a Proxy Re-Signature (PRS) algorithm designed by NuCypher called Penumbral.

The NuBLS library offers bindings to Python from a rust backend, see below for details.

Rust

The core of NuBLS is written in Rust, and is accessible here - https://github.com/nucypher/NuBLS/tree/master/rust-nubls

Python

The Python bindings are also written in Rust using the PyO3 library to ensure safety. This crate is accessible here - https://github.com/nucypher/NuBLS/tree/master/nubls/src

Installation

You can install NuBLS from pip with: pip install pynubls. Alternatively, see the build instructions below.

Building PyNuBLS

To build pynubls for Python, create a virtual environment and install maturin: pip install maturin

Then build the package with: maturin build

To build and install the package into your virtual environment use: maturin develop

Usage

The API for the Python wrapper closely resembles that of the Rust API. After installing via pip or building the development version, you can call it in Python with:

from pynubls import PrivateKey, PublicKey, hash_message, InvalidSignature

priv_key = PrivateKey.random()
pub_key = priv_key.public_key()

priv_key_bytes = priv_key.to_bytes()
pub_key_bytes = pub_key.to_bytes()

# Splitting/Recovery
key_frags = priv_key.split(3, 5)
recovered_key = PrivateKey.recover(key_frags[:3])

# Signing
sig = priv_key.sign(hash_message(b'NuBLS!'))
try:
    pub_key.verify(hash_message(b'NuBLS!'), sig)
except InvalidSignature:
    # Raises `InvalidSignature` when the signature is invalid.
    print("The signature is invalid.")

# Penumbral Proxy Re-Signature
alice_priv, bob_priv = PrivateKey.random(), PrivateKey.random()

resigning_key_bob_to_alice = alice_priv.resigning_key(bob_priv.public_key())
sig_under_bob = bob_priv.designated_key(alice_priv.public_key()).sign(hash_message(b'Penumbral!'))

resigned_sig = resigning_key_bob_to_alice.resign(sig_under_bob)
alice_priv.public_key().verify(hash_message(b'Penumbral!'), resigned_sig)

Warning

As this library is a work-in-progress, there are some missing API details. One of these is a rust-native hash-to-curve implementation. As such, it's not presently possible to hash messages natively with this library, and another library must be used. To get around this, pynubls uses the py-ecc library for hashing messages to the curve.