ZKVM with Circom and SnarkJS (Simple Stack Based zkVM)

This repository demonstrates how to build and test a simple Zero-Knowledge Virtual Machine (ZKVM) using Circom for circuit design and SnarkJS for generating and verifying zk-SNARK proofs.

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📦 Prerequisites

Ensure you have the following installed:

• Node.js (>= 16.x)

• npm (comes with Node.js)

• Circom v2 (installation guide)

• SnarkJS (install globally)

    Sudo npm install -g snarkjs

• Vim or any text editor (for editing input.json)

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⚙️ Project Setup

Clone this repo and install dependencies:

git clone <your-repo-url>
cd <your-repo>

Project Structure

zkvm.circom       # The main Circom circuit file
input.json        # Input values for witness generation
README.md         # This documentation

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📝 Step 1: Write Circuit (zkvm.circom)

Example zkvm.circom:

include "node_modules/circomlib/comparators.circom";

// Simple stack-based VM logic here
component main = ... ;

⚠️ If you use external libraries (like circomlib), make sure they are installed:

npm install circomlib

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📝 Step 2: Define Inputs (input.json)

Create an input.json file with Vim or another editor:

vim input.json

Example content:

{
  "instr": [1,3,1,6,1,2,3,0,3,0]
}

Save and exit with :wq.

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⚡ Step 3: Compile the Circuit

circom zkvm.circom --r1cs --wasm --sym -l node_modules/circomlib/circuits

This generates:

• zkvm.r1cs → circuit constraints
• zkvm_js/ → witness generation code
• zkvm.sym → symbols file

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🛠️ Step 4: Generate Witness

Run:

node zkvm_js/generate_witness.js zkvm_js/zkvm.wasm input.json witness.wtns

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🔑 Step 5: Trusted Setup

5.1 Powers of Tau

Initialize:

snarkjs powersoftau new bn128 12 pot12_0000.ptau -v

Contribute:

snarkjs powersoftau contribute pot12_0000.ptau pot12_0001.ptau --name="First contribution" -v

Prepare for phase 2:

snarkjs powersoftau prepare phase2 pot12_0001.ptau pot12_final.ptau -v

5.2 Circuit-specific Setup

snarkjs groth16 setup zkvm.r1cs pot12_final.ptau zkvm_0000.zkey

Add contribution:

snarkjs zkey contribute zkvm_0000.zkey zkvm_final.zkey --name="Key Contributor" -v

Export verification key:

snarkjs zkey export verificationkey zkvm_final.zkey verification_key.json

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✅ Step 6: Generate Proof

snarkjs groth16 prove zkvm_final.zkey witness.wtns proof.json public.json

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🔍 Step 7: Verify Proof

snarkjs groth16 verify verification_key.json public.json proof.json

Expected output:

OK!

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🌐 Step 8: Export Solidity Verifier (Optional)

snarkjs zkey export solidityverifier zkvm_final.zkey Verifier.sol

Compile and deploy Verifier.sol to Ethereum or compatible chains to perform on-chain verification.

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📚 Troubleshooting

• EACCES: permission denied, mkdir '/usr/local/lib/node_modules' → Install with sudo or configure npm prefix:

  mkdir ~/.npm-global
  npm config set prefix '~/.npm-global'
  export PATH=~/.npm-global/bin:$PATH

• The file circomlib/comparators.circom not found → Add include path -l node_modules/circomlib/circuits

• [ERROR] snarkJS: Powers of tau is not prepared → Run Phase 1 & Phase 2 trusted setup first.

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📖 References

• Circom Documentation
• SnarkJS GitHub
• Awesome Zero-Knowledge

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🚀 You now have a working ZKVM setup with Circom + SnarkJS!