ZK VoCeremony

This repo contains a toolkit for creating and contributing to a zk ceremony, using this repo to track the whole process in a separate branch for each ceremony.

The toolkit only supports Circom circuits, and only makes sense for proving systems that require a specific trusted ceremony (e.g. Groth16). It uses Circom to compile the circuits and SnarkJS to generate the circuit artifacts, create ceremonies and perform contributions.

Trusted Ceremonies

A zk ceremony o trusted ceremony, is a multy-party computation process to generate the required inputs to use a zk snark circuit in a secure and reliable way, a trusted setup. This trusted setup includes two resulting keys:

• The proving key: Used to generate zk proofs using the circuit for which it was generated.
• The verifiying key: Used to verify these proofs.

This process also produces a piece of data called toxic waste which must be discarded, as it can be used to generate fake proofs. And this is because it is performed as a multy-party computation, to reduce the risks of the process distributing it in multiple participants.

In turn, each party takes the previous contribution (starting from an initial one generated during the creation of the ceremony) and contributes with a random input to generate entropy at the output. Then, the result of the process is uploaded and the toxic-waste is discarded.

The process can be repeated through the participants in rounds until the ceremony ends (the number of rounds is determined during the ceremony creation process).

You can read more about trusted zk ceremonies here.

How to use the toolkit?

• Requirements
• Contribute to a ceremony
• Create a new zk-ceremony

Requirements

• Git and a Github account with permissions push to non main branches of this repository. The process will be stored and tracked in a branch of the current GitHub repository. A verified signature must be configured with git to sign the resulting commits.
• Docker: The toolkit uses docker containers to avoid installing dependencies on the host machine and to avoid incompatibilities.
• Git LFS installed and initialized (only to create a ceremony) to track large files like contribution files.

Contribute to a ceremony

You just need docker run, the image will clone this repository and guide you through the whole process:

docker run --rm -it vocdoni/zk-voceremony

This will create:

• {CONTRIBUTIONS_PATH}/{circuite_name}_{contributor_alias}.zkey: The result of your contribution.

And will update:

• {CONTRIBUTIONS_PATH}/CONTRIBUTIONS.md: Add your contribution filename and checksum to the list of contributions and set it as the last contribution.

Checkout a demo of a contribution process

Create a new zk-ceremony

Run the following command to prepare the environment:

git clone https://github.com/vocdoni/zk-voceremony.git && cd ./zk-voceremony
bash ./scripts/create-env.sh

This will create the ceremony.env following the example.env template, asking to you the required inputs. Then it will copy from your filesystem into the repo:

• {INPUTS_PATH}/{circuite_name}.circom: the circom circuit file target of the ceremony
• {INPUTS_PATH}/{initial_ptau}.ptau: the initial ptau file

It also will create the ceremony branch, commit and push these files to this branch.

A Github action will compile the circuit and generate the first contribution in the {ceremony_name} branch. This Github will also create an Pull Request assigned to you. If this PR is closed by you (without merge it), another Github action will be triggered that will finish the ceremony and generate the final artifacts.

Other options

Build docker images locally

docker build . --target zk-voceremony --tag vocdoni/zk-voceremony
docker build . --target zk-voceremony-create --tag vocdoni/zk-voceremony-create