zk-sbt

This repository is an example of how zK-Snarks can be combined with the concept of Soul Bound Token.

This follows part 3 of Spartan Labs Soul Bound Token Article series:

• Part 1: The ABCs of SBT
• Part 2: Implementations of SBT
• Part 3: zkSBT

Demo of ZKSBT

For demo purposes of the toy example, we have included the next.js folder over at client/

For the server, we have included the express server over at server/

To run the application, just run npm install and then npm run dev in both the client/ and npm start for the server/ folders.

To generate the following contract by yourself, you can refer to the instructions below:

Installing Dependencies

Clone this repository

git clone https://github.com/SpartanLabsXyz/zk-sbt.git

yarn to install dependencies

Install Circom 2 from https://github.com/iden3/circom

Dependencies version

• node : 16.16
• snarkjs: 0.4.25
• circom v2: 2.0.3

Folder setup

client/ : contains demo code where we can run our prover server/: contains the endpoints for proof generation and call data generation contracts/ : contains Verifier.sol which allows us to prove attributes about SBT

Files for zkSBT

contracts/Verifier.sol

• This file is autogenerated by snarkjs.
• For our zkSBT contract, we would be using Verifier.sol for proving that a given SBT has valid attributes using verifyProof.
• verifyProof is a function that takes in a calldata and a proof and returns a boolean.

zk-SNARKS Setup

yarn circom:dev to build deterministic development circuits.

Further, for debugging purposes, you may wish to inspect the intermediate files. This is possible with the --debug flag which the circom:dev task enables by default. You'll find them (by default) in artifacts/circom/

To build a single circuit during development, you can use the --circuit CLI parameter. For example, if you make a change to hash.circom and you want to only rebuild that, you can run yarn circom:dev --circuit hash.

Production builds

yarn circom:prod for production builds (using Date.now() as entropy)

Our Setup with Powers Of Tau and Groth16

Run sh execute.sh for the step by step setup

For more information on setting up, visit Their README

Using the app

npm -i # installs all dependencies

Run app/index.html

The script for proving is in app/index.js

Circom Commands

Compile Circuits

circom circuit.circom --r1cs --wasm --sym

Options:

--r1cs: generates circuit.r1cs (the r1cs constraint system of the circuit in binary format).

--wasm: generates circuit.wasm (the wasm code to generate the witness – more on that later).

--sym: generates circuit.sym (a symbols file required for debugging and printing the constraint system in an annotated mode).

View information on circuit

• look at some of the information circuit.r1cs : snarkjs info -r circuit.r1cs

• print constraints: snarkjs printconstraints -r circuit.r1cs -s circuit.sym

you can ignore the 1main prefix and just read this as:

(-a) * b - (-c) = 0

Which, if you rearrange the equation, is the same as a * b = c.

Trusted Setup using snark.js

The need for a trusted setup boils down to the fact that the balance between privacy for the prover, and assurance of not cheating for the verifier, is delicate.

snarkjs setup -r circuit.r1cs : This will generate both a proving and a verification key in the form of two files: proving_key.json and verification_key.json.

Contract deployment

1. Compile contracts
2. Deploy and verify

Architecture

Credits

A Zero Knowledge Soul Bound token project using starter developed by Blaine & Brian:

• using Hardhat
• hardhat-circom.

This combines the multiple steps of the Circom and SnarkJS workflow into your Hardhat workflow.

By providing configuration containing your Phase 1 Powers of Tau and circuits, this plugin will:

1. Compile the circuits
2. Apply the final beacon
3. Output your wasm and zkey files
4. Generate and output a Verifier.sol