ZK Integration Workflow:

Step 1: Compile the Circuit

• Use the Circom compiler to generate the circuit artifacts with the following flags:

  circom <circuit>.circom --r1cs --c --no<-asm -O0  # or -O1 / -O2
  

• Try different optimization levels (O0, O1, O2) and select the one that yields the fewest constraints.

• This compilation is done once per circuit and is not included in the node's runtime.

Step 2: Generate Proving and Verification Keys

• Use snarkjs with the compiled .r1cs file and a trusted Common Reference String (CRS) to generate:

  • A .zkey file (proving key)
  • A verification_key.json file (verifying key)

• Example command:

  
  snarkjs groth16 setup <circuit>.r1cs <ptau_file>.ptau <circuit>.zkey
  snarkjs zkey export verificationkey <circuit>.zkey verification_key.json
  
  

• The .zkey is passed to the prover, and the verification key is hardcoded in the node.

• Verification can be performed using Arkworks, implementing a Groth16 verifier with the verification key values embedded.

Step 3: Compile and Integrate the Witness Generator

• Compile the C++ code generated by Circom (from Step 1) to produce a binary witness generator.
• Each circuit requires a dedicated witness generator binary.
• Ensure:
  • Optimization flags used during compilation are publicly documented.
  • The compiled witness generator is portable and transparent for reproducibility.
• This binary is integrated into the node and called when a witness must be generated.

Step 4: Generate the ZK Proof

• Use Rapidsnark to generate a Groth16 proof.

• Input:

  • The .zkey proving key
  • A .wtns file (witness) generated from the circuit + input values

• Output:

  • proof.json: the zero-knowledge proof
  • public.json: the public inputs and outputs

• Example command:

  
  rapidsnark <circuit>.zkey <witness>.wtns