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BLS Horcrux

Introduction

bls-horcrux is a tool for creating a threshold BLS key in a trustless manner. It uses Shamir's secret sharing and BLS properties to create a key that is shared between m parties and requires n out of m signatures to reconstruct the final signature.

Installation

Prerequisites

Option 1. Build bls-horcrux with native Python

pip3 install -r requirements/prod.txt

Or use the helper script:

./horcrux.sh install

Option 2. Build bls-horcrux with virtualenv

For the virtualenv users, you can create a new venv:

python3 -m venv venv
source venv/bin/activate

and install the dependencies:

pip install -r requirements/prod.txt

Option 3. Build the docker image

Run the following command locally to build the docker image:

docker build --pull -t bls-horcrux .

Preparation

Common

Before BLS horcruxes can be generated, their holders must agree on the following:

  • Participants - who are the holders of the horcruxes and how many there will be in total.
  • Threshold - the minimum number of BLS signatures required to reconstruct the final signature.
  • Dispatcher - what endpoint should be used for the horcruxes to communicate (See dispatcher).
  • Offline PC - a PC which is isolated from the Internet, where the final horcrux will be generated.
  • Online PC - a PC which is connected to the Internet and is used for interacting with the dispatcher.

Individual

Choose how would you like to execute the commands required to generate your horcrux:

  • Shell script (the examples below will be given using this method): 
    ./horcrux.sh <command>
  • Python: 
    python3 horcrux.py <command>
  • Docker: 
    docker run -it --rm -v $(pwd)/data:/app/data bls-horcrux <command>

Creating horcrux

To create the BLS horcrux every participant must execute the following command and follow the steps after:

./horcrux.sh create-rsa-key
linux-gnu
Running BLS horcrux...
Enter path to the file where the RSA private key should be saved [/bls-horcrux/data/rsa_key.pem]: 
Generating RSA key for communicating with other horcruxes...


ssh-rsa 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


Enter the password that secures your RSA key: 
Repeat for confirmation: 
Saved RSA private key to /bls-horcrux/data/rsa_key.pem
Next steps:
1) Share the RSA public key above with all other participants.
2) Paste yours and other participants' RSA public keys to
   /bls-horcrux/data/all_rsa_public_keys.txt file.
   NB! The file must be equal for all the participants.
3) Run ./horcrux.sh create-bls-key on your offline PC.

Signing data

To sign a message, call the command below and pass all the required parameters:

./horcrux.sh sign --horcrux-file /bls-horcrux/data/horcrux0.json
linux-gnu
Running BLS horcrux...
Enter the horcrux password used during your horcrux creation: 
Enter hexadecimal encoded data to sign: 0x48656c6c6f20576f726c6421
Signature: 0x91f5c9ce5cee0b1953649fe5f57672d295f654ec7930e2d7bbafed03df5bfadd42a75a5bbf977b0ed17af05244f72063017257cd31d0f9f16409fa188f2dad784821bbc7e507b70c20c97630abf52d781a812f4edfd317b1b1220abc2fdd491b
Horcrux index: 0
Next steps:
1) Retrieve signatures of the same signing data from other horcruxes.
2) Run ./horcrux.sh reconstruct-signature to reconstruct the final signature.
   NB! At least 3 signatures are required to reconstruct.

Reconstructing threshold signature

To reconstruct a final signature, collect signatures and indexes from other horcruxes (as in the section above) and call:

./horcrux.sh reconstruct-signature
darwin19
Running BLS horcrux...
Enter the total number of BLS signatures to reconstruct the final signature from: 3
Enter the horcrux index of the submitted signature (can be found in the owner's horcrux file): 0
Enter the next hexadecimal encoded BLS signature (1/3): 0x88dbee76bca22f82f56bd846f3b2844975191b87dc9cd9fa1823a5fa33607eb188d8dcb4d46e06c69358a7e407c1f3a40c9cece031e8f45259c9731b5e24a32704ef60781a3de1663e2a12a136c9de54e5202f72dc8783afa3180d33258a5528
Enter the horcrux index of the submitted signature (can be found in the owner's horcrux file): 3
Enter the next hexadecimal encoded BLS signature (2/3): 0xa1da37d002e282837198ecad02ffc8b5aaf9ecf5260b04659d8544383defbf6b7518a9ca06f1d0ece6c84935e50816cf0211867e681e3a179db26b3c28a14c1ea25983a703a0e06fac336b29d7e88e98414edbd736bd83b0d9b68c99201aab87
Enter the horcrux index of the submitted signature (can be found in the owner's horcrux file): 1
Enter the next hexadecimal encoded BLS signature (3/3): 0x80e9b13f5a81e678d797b59c76e70c1d8bc385a6d253917a651a7738487a7ab8bd70f6246e8adfeb0f22a35eb4f6eab61474c7f6d73bf68456f4fe04ce9055e302de86cd3186993ac86c77dacc38ed3d648c57d602f903071253439e7cff158b
Reconstructed signature: 0xad9c32db5ba78df50b058c4b659ec1f708e1c6f821c163e1dc60a9e54dcb7f575d44083c8de3dda188fe7a2c9c641a7c00b11136c6dc1cbd6a851d1087e88d18c0b5a59229073e885dde8358e44459c68c8b8bfdaf5e60853238451ce7264d4d
Run ./horcrux.sh verify-signature to verify whether the signature is correct.

NB! Number of signatures should be at least equal to the amount specified in threshold from step 1 of Creating Horcrux section. The data signed must be the same for all the participants.

Verifying threshold signature

To verify the signature, copy the value of the shared BLS public key (shared_public_key) from the horcrux keystore and call:

./horcrux.sh verify-signature
darwin19
Running BLS horcrux...
Enter the hexadecimal encoded shared BLS public key to verify (can be found in horcrux file): 95dbbf215b9fd18c797f309b95f6eff5756c0e8edf474adfff0358ac25cdcff3aacae8d8e51dc4807a1cd8e99c053c57
Enter the hexadecimal encoded signing data: 0x48656c6c6f20576f726c6421
Enter the hexadecimal encoded BLS signature to verify: 0xad9c32db5ba78df50b058c4b659ec1f708e1c6f821c163e1dc60a9e54dcb7f575d44083c8de3dda188fe7a2c9c641a7c00b11136c6dc1cbd6a851d1087e88d18c0b5a59229073e885dde8358e44459c68c8b8bfdaf5e60853238451ce7264d4d
[+] The signature is valid