How to use TypedDataHash to make a transaction?

Question

I am trying to make a Meta Transaction without using the conventional TypedData object. Instead I have used ethers.utils._TypedDataEncoder.hash to create the hash.

I signed the hash using the ethereumjs-util and eth-sig-util packages but want a different approach to create the signature.

Now I am not sure how to use the hash without using the ethereumjs-util and eth-sig-util packages but rather the signer created using the private key (const walletSigner = new ethers.Wallet(PRIVATE_KEY, provider)).

const signature = await walletSigner.sign(hash)

Something like the above which will create a valid signature.

Please let me know if the hash can be signed using the web3.js Javascript Ethereum API.

Answer 1

for meta transaction you have 3 steps :

1-Implement the signature function in your smart contract and pass your values to it. it use "_hashTypedDataV4" and "keccak256", like below:

function hashGenerator(YourStruct memory yourStruct)
    internal
    view
    returns (bytes32)
{
    return
        _hashTypedDataV4(
            keccak256(
                abi.encode(
                    keccak256(
                        "YourStruct(address x,uint256 y)"
                    ),
                    yourStruct.x//x value 
                    yourStruct.y//y value
                    
                )
            )
        );
}

2-in web3 you must do the same in sign values, like this

 const signature = await signer._signTypedData(
  // Domain
  {
    name: "nameOfYourContract",
    version: "1.0",//your version
    chainId: yourchainID,
    verifyingContract: this.yourContract,
  },
  // Types
  {
    YourStruct: [
      { name: "x", type: "address" },
      { name: "y", type: "uint256" },
    ],
  },
  // Values
  {
   x_value,
   y_value
  } //
);

3-in the last step you have to compare web3 signature with your smart contract signature to prove it.

  function signVerify(
    YourStruct memory yourStruct,
    bytes calldata signature
) internal view returns (address) {
    bytes32 digest = hashGenerator(yourStruct);
    return ECDSAUpgradeable.recover(digest, signature);
}

for better understanding, I recommend to read this link.