Zero-Knowledge Proof of SHA256 Hash using zkSNARK

This article provides you sufficient commands to run zkSNARK algorithm with circom circuits on a Ubuntu Docker image to prove SHA256 hash.

If you are just testing for educational purposes, I recommend to use Docker for cleaner setup. However, if you wish to run the zkSNARK program on your machine, you can start from Install Prerequisites section.

Setup Ubuntu Instance on Docker

1. docker run -it ubuntu:jammy
2. apt update
3. apt install curl
4. apt install nano

Install Prerequisites

1. apt install build-essential
2. curl --proto '=https' --tlsv1.2 https://sh.rustup.rs -sSf | sh (proceed with standard installation)
3. . "$HOME/.cargo/env"
4. curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.7/install.sh | bash
5. nvm install 20
6. export NVM_DIR="$HOME/.nvm"
7. [ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh"
8. apt install git-all
9. git clone https://github.com/iden3/circom.git
10. cd circom
11. cargo build --release
12. cargo install --path circom
13. npm install -g snarkjs

Develop and Run the zkSNARK Program

1. Create program.circom file by running nano program.circom

pragma circom 2.0.0;
include "./circomlib/circuits/sha256/sha256.circom";

template program() {
    signal input in[2];
    signal output out[256];

    component SHA = Sha256(2);
    SHA.in <== in;
    out <== SHA.out;
}

component main = program();

2. Get sha256 library by simply running git clone https://github.com/iden3/circomlib.git in project directory.

Pro tip: Similarly you can use other given libraries to write any custom program for your scenario

3. Compile the .circom file using circom program.circom --r1cs --wasm --sym --c.