Verifier contract

vlayer provides Verifier smart contracts that allow on-chain verification of computations performed by Prover contracts. To use the output computed by Prover contract, follow the rules covered in the next section.

Proof Verification

Proof verification can be done by any function that uses the onlyVerified modifier and passes arguments in a particular way. We call such a function verification function. See the example below, with verification function claim.

contract Example is Verifier {

    function claim(
      Proof _p, 
      address verifiedArg1, 
      uint verifiedArg2, 
      bytes extraArg
    ) 
      public 
      returns (uint)
      onlyVerified(PROVER_ADDRESS, FUNCTION_SELECTOR) 
    {
        //...
    }
}

onlyVerified modifier

The onlyVerified modifier takes two arguments:

  1. Prover contract address
  2. the signature of the Prover function used to generate the proof

Under the hood, onlyVerified reads the submitted Proof and public inputs from msg.data. It ensures that:

  • The proof is valid and passes verification
  • The public inputs match values returned from Prover
  • The proof was created by the specified Prover contract and the specified function This prevents invalid, tampered, or mismatched proofs from being accepted by the contract.

Proof argument

Passing Proof as the first argument to the verification function is mandatory. Note that even though the proof is not used directly in the body of the verified function, onlyVerified will have access to it via msg.data.

Verified arguments

After the proof, we need to pass verified arguments. Verified arguments are the values returned by the Prover contract function. We need to pass all the arguments returned by prover, in the same order and each of the same type.

See the example below.

contract Prover {

  function p() return (Proof p, address verifiedArg1, uint256 verifiedArg2, bytes32 verifiedArg3) {
    ...
  }
}

contract Verifier {
  function v(Proof _p, address verifiedArg1, uint256 verifiedArg2, bytes32 verifiedArg3) 
}

Note: Passing different variables (in terms of type, name, or order) would either revert execution or cause undefined behavior and should be avoided for security reasons.

Extra arguments

Extra arguments can be passed to Verifier by using additional function. This function manages all additional operations connected with extra arguments and then calls the actual verification function.

See the example below:

function f(Proof _p, verifiedArg1, verifiedArg2, extraArg1, extraArg2) {
  ...
  v(_p, verifiedArg1, verifiedArg2);
}