The full pipeline — setup, prove, verify, solidity

hard

Learn with your AI

Open this lesson in your favourite AI. It'll walk you through the why, explain the demo, and quiz you on the try-it list.

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Why this matters

Writing a circuit is 20% of the work. The other 80% is the SNARK pipeline: running a trusted setup (Powers of Tau ceremony), generating a circuit-specific key, producing proofs, and (for blockchain apps) generating a Solidity verifier and deploying it. This task walks through the full shell-command pipeline for a minimal circuit, end to end, so you have the reps when it comes time to ship.

Demo

Complete pipeline for the Multiplier circuit from Task 1. Five shell commands: powers-of-tau (reuse an existing ceremony output), circuit-specific setup (phase 2), prove, verify, export-Solidity. Total time for a tiny circuit: under 2 minutes.

# Full Groth16 pipeline for multiplier.circom
# Prereqs: circom 2.x, snarkjs 0.7+, powers-of-tau ptau file
 
# 1) Compile circuit
circom multiplier.circom --r1cs --wasm --sym -o build/
 
# 2) Setup (phase 2 — circuit-specific)
#    Assume powersOfTau28_hez_final_10.ptau exists from hermez ceremony
snarkjs groth16 setup build/multiplier.r1cs \
  powersOfTau28_hez_final_10.ptau \
  build/multiplier_0000.zkey
 
#    Contribute randomness to phase 2 ceremony
snarkjs zkey contribute build/multiplier_0000.zkey \
  build/multiplier_final.zkey --name="alice" -v
 
#    Export verification key
snarkjs zkey export verificationkey build/multiplier_final.zkey \
  build/verification_key.json
 
# 3) Generate witness for input {a:3, b:11}
echo '{"a":"3","b":"11"}' > input.json
node build/multiplier_js/generate_witness.js \
  build/multiplier_js/multiplier.wasm input.json build/witness.wtns
 
# 4) Prove
snarkjs groth16 prove build/multiplier_final.zkey \
  build/witness.wtns build/proof.json build/public.json
 
# 5) Verify locally
snarkjs groth16 verify build/verification_key.json \
  build/public.json build/proof.json
# → OK
 
# 6) Generate Solidity verifier contract
snarkjs zkey export solidityverifier build/multiplier_final.zkey \
  build/Verifier.sol
# → Verifier.sol has verifyProof() — inherit or deploy directly

Try it yourself

Run the full pipeline on multiplier.circom from Task 1. Time each step. Observe that 'setup' is the slow one (10–60 seconds for a tiny circuit; minutes for large ones).

Export the Solidity verifier. Deploy it to a Sepolia or Anvil testnet. Submit a valid proof from within Hardhat/Foundry and confirm it verifies on-chain. The gas cost for Groth16 verify is ~200k.

Run snarkjs zkey beacon with a public randomness beacon (e.g., a recent block hash) as a final ceremony contribution. This is standard practice for production ceremonies.

Try verifying a tampered proof (flip one byte in proof.json). snarkjs rejects it. This is what the on-chain verifier also does.

Measure the difference between Groth16 and PLONK on the same circuit: snarkjs plonk setup / prove / verify. PLONK has universal setup, slightly larger proofs, but more flexibility. Understand when to pick each.

Prompt your AI

Use these three in order. Each builds on the one before.

1. Basics & terminology

In one paragraph, walk me through the end-to-end Circom → SNARK → on-chain pipeline: compile, setup, witness-gen, prove, verify, deploy.

2. Why it works (the mechanism)

Walk me through the two-phase setup for Groth16: what does the Powers of Tau ceremony produce, what's specific to a given circuit in phase 2, and why is the ceremony 'trusted' — what happens if someone records the toxic waste?

3. Advanced — application & what's next

I'm deploying a production zk-SNARK verifier contract on Ethereum. Walk me through: (a) which ptau file is safe to use (and who ran it), (b) how I'd organise my own phase-2 ceremony with multiple contributors, (c) how I'd optimise gas on the Solidity verifier.