ZKVote

Anonymous on-chain voting using Zero Knowledge proofs. Voters prove membership in a Merkle tree without revealing their identity. Double-voting is prevented via nullifiers.

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How It Works

1. Each eligible voter has a secret whose hash is a leaf in a Merkle tree
2. To vote, the voter generates a ZK proof that they know a secret in the tree — without revealing which leaf
3. A nullifier derived from the secret is recorded on-chain to prevent voting twice
4. The proof is verified by a Solidity contract generated by Barretenberg

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Prerequisites

Tool	Version	Install
Nargo (Noir)	1.0.0-beta.20	See below
Barretenberg (bb)	4.2.0	See below
Node.js	18+	nodejs.org
Remix IDE	—	remix.ethereum.org

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Installation

1. Install Nargo (Noir)

curl -L https://raw.githubusercontent.com/noir-lang/noirup/main/install | bash
noirup --version 1.0.0-beta.20

Verify:

nargo --version

2. Install Barretenberg (bb)

curl -L https://raw.githubusercontent.com/AztecProtocol/aztec-packages/master/barretenberg/bbup/install | bash
bbup --version 4.2.0

If bbup fails, install manually:

curl -L -o /tmp/bb.tar.gz https://github.com/AztecProtocol/aztec-packages/releases/download/v4.2.0/barretenberg-amd64-linux.tar.gz
mkdir -p ~/.bb
tar -xzf /tmp/bb.tar.gz -C ~/.bb/
chmod +x ~/.bb/bb

Verify:

bb --version

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Usage

1. Compile the circuit

nargo compile

2. Generate a witness

Edit Prover.toml with your inputs, then:

nargo execute

3. Generate the verification key

mkdir -p ./target/vk
bb write_vk -b ./target/zkvote.json -o ./target/vk -t evm

4. Generate a proof

bb prove -b ./target/zkvote.json -w ./target/zkvote.gz -k ./target/vk/vk -o ./target/proof -t evm

5. Export proof as hex (for on-chain use)

python3 -c "
with open('./target/proof/proof', 'rb') as f:
    data = f.read()
print('0x' + data.hex())
"

6. Generate Solidity verifier

bb write_solidity_verifier -k ./target/vk/vk -o ./target/HonkVerifier.sol

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Deployment (Remix IDE)

1. Open remix.ethereum.org
2. Upload HonkVerifier.sol and ZKVote.sol
3. Compile both with Solidity ^0.8.20
4. Deploy HonkVerifier first — copy its address
5. Deploy ZKVote with:
   • _verifier: HonkVerifier address
   • _merkleRoot: your Merkle root
   • _startTime: voting start (unix timestamp)
   • _endTime: voting end (unix timestamp)
6. Call castVote with your proof hex, nullifier, and vote (0 or 1)

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Prover.toml Format

secret = "42"          # your private secret
vote = "1"             # 0 = against, 1 = for
index = "0"            # leaf index in the Merkle tree
path = ["1", "2", "3"] # sibling hashes along the Merkle path
merkle_root = "0x..."  # public Merkle root
nullifier = "0x..."    # public nullifier (pedersen_hash([secret]))

To get the correct merkle_root and nullifier for your inputs:

nargo test --show-output

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Project Structure

zkvote/
├── src/
│   └── main.nr          # Noir circuit
├── Nargo.toml           # Noir project config
├── Prover.toml          # Witness inputs
├── ZKVote.sol           # Voting contract
└── HonkVerifier.sol     # Auto-generated ZK verifier

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License

MIT