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Quick Start

Generate your first zero-knowledge proof in under 5 minutes!

Your First Proof​

Let's prove that someone is over 18, has sufficient balance, and is from an allowed country - without revealing their actual age, balance, or location.

  1. Run the Demo
cd openzktool
npm run demo:privacy

2. What Just Happened?​

The demo:

  1. Generated a proof with private inputs (age: 25, balance: $150, country: Argentina)
  2. Verified constraints: age ≥ 18, balance ≥ $50, country in allowed list
  3. Output: kycValid = 1 (passed) ✓

The magic: The verifier knows requirements are met, but NOT the actual values!

Manual Proof Generation​

Want to generate proofs programmatically? Here's how:

Step 1: Create Input File​

Create my_input.json:

{
  "age": "25",
  "balance": "150",
  "country": "11",
  "minAge": "18",
  "maxAge": "99",
  "minBalance": "50",
  "allowedCountries": ["11", "1", "5", "0", "0", "0", "0", "0", "0", "0"]
}

Note: All values are strings (Circom requirement).

Step 2: Generate Proof​

npm run prove

This creates:

  • circuits/build/proof.json - The ZK proof (800 bytes)
  • circuits/build/public.json - Public outputs (kycValid)

Step 3: Verify Locally​

snarkjs groth16 verify \
  circuits/build/verification_key.json \
  circuits/build/public.json \
  circuits/build/proof.json

Output: [INFO] snarkJS: OK! ✓

Verify on Stellar Soroban​

Now let's verify the proof on-chain using our deployed contract:

npm run demo:soroban

This:

  1. Connects to Stellar testnet
  2. Calls the verifier contract
  3. Returns verification result

Contract: CBPBVJJW5NMV4UVEDKSR6UO4DRBNWRQEMYKRYZI3CW6YK3O7HAZA43OI

Understanding the Flow​

sequenceDiagram
    participant User
    participant Circuit
    participant Prover
    participant Soroban

    User->>Circuit: Private data (age, balance, country)
    Circuit->>Prover: Generate proof
    Prover->>User: 800-byte proof
    User->>Soroban: Submit proof
    Soroban->>User: Verified ✓ (data stays private)

What's in a Proof?​

A proof consists of three elliptic curve points:

{
  "pi_a": ["...", "..."],     // Point A on curve
  "pi_b": [["...", "..."]],   // Point B on curve
  "pi_c": ["...", "..."],     // Point C on curve
  "protocol": "groth16",
  "curve": "bn128"
}

Size: ~800 bytes (constant, regardless of input complexity!)

Common Use Cases​

Age Verification (18+)​

cat > age_check.json << EOF
{
  "age": "22",
  "balance": "0",
  "country": "0",
  "minAge": "18",
  "maxAge": "99",
  "minBalance": "0",
  "allowedCountries": ["0", "0", "0", "0", "0", "0", "0", "0", "0", "0"]
}
EOF

# Generate proof
snarkjs groth16 fullprove age_check.json \
  circuits/build/kyc_transfer_js/kyc_transfer.wasm \
  circuits/build/kyc_transfer_final.zkey \
  proof.json \
  public.json

Minimum Balance Check​

cat > balance_check.json << EOF
{
  "age": "0",
  "balance": "5000",
  "country": "0",
  "minAge": "0",
  "maxAge": "999",
  "minBalance": "1000",
  "allowedCountries": ["0", "0", "0", "0", "0", "0", "0", "0", "0", "0"]
}
EOF

Geographic Compliance​

cat > geo_check.json << EOF
{
  "age": "0",
  "balance": "0",
  "country": "1",
  "minAge": "0",
  "maxAge": "999",
  "minBalance": "0",
  "allowedCountries": ["1", "5", "11", "0", "0", "0", "0", "0", "0", "0"]
}
EOF

Performance​

Typical timings on modern hardware:

OperationTime
Proof generation< 1 second
Local verification< 50ms
On-chain verification~200ms

Troubleshooting​

"WASM file not found"​

Make sure you ran npm run setup first to compile circuits.

"Invalid witness"​

Check that all input values are strings and within valid ranges.

"Verification failed"​

Ensure public inputs match between proof generation and verification.

Next Steps​

Questions? Ask on GitHub Discussions