How to use nonce to prevent signature replication?

Question

I would like to verify that a message is sent by a certain address, and to get the signer address I use the following function:

function VerifyMessage(bytes32 _hashedMessage, uint8 _v, bytes32 _r, bytes32 _s) public pure returns (address) {
    bytes memory prefix = "\x19Ethereum Signed Message:\n32";
    bytes32 prefixedHashMessage = keccak256(abi.encodePacked(prefix, _hashedMessage));
    address signer = ecrecover(prefixedHashMessage, _v, _r, _s);
    return signer;
}

But in order to prevent the replication of the signature I would like to use nonce. How can I integrate the nonce into my logic? I have also frontend and backend in my application if any management might be required from those sides.

Answer 1

You can have a look at how the permit function in the ERC20 is implemented: https://github.com/fractional-company/contracts/blob/master/src/OpenZeppelin/drafts/ERC20Permit.sol#L57-L60

Basically you need to have a mapping (address => uint256) public nonces; in your contract, that saves the last used nonce for every signer.

The signer must sign a message that contains the current nonce, so you have to add nonces[msg.sender] inside abi.encodePacked(prefix, _hashedMessage). I'm using msg.sender, but of course if you're checking against another user you need to pass its address.

Putting it all together:

function VerifyMessage(bytes32 _hashedMessage, uint8 _v, bytes32 _r, bytes32 _s) public pure returns (address) {
    bytes memory prefix = "\x19Ethereum Signed Message:\n32";

    bytes32 prefixedHashMessage = keccak256(abi.encodePacked(
        prefix,
        nonces[msg.sender],
        _hashedMessage
    ));
    address signer = ecrecover(prefixedHashMessage, _v, _r, _s);

    require(msg.sender == signer);
    nonces[msg.sender] += 1;

    return signer;
}