Off-chain generation of signature using Ethers.js and on-chain verification

index.js

import { ethers } from 'ethers';

const signerPrivateKey = "0x900edb9e8214b2353f82aa195e915128f419a92cfb8bbc0f4784f10ef4112b86";
const signer = new ethers.Wallet(signerPrivateKey);

const nonce = 'hello';

const signature = await signer.signMessage(nonce);

// The recovered address should be the same than the signer address
console.log('Address:', signer.address);
console.log(
  'Recovered address:',
  ethers.utils.recoverAddress(ethers.utils.hashMessage(nonce), signature),
);

const nonceHex = ethers.utils.hexlify(ethers.utils.toUtf8Bytes(nonce);

// These are the arguments of verifySignature smart-contract method
console.log('nonce:', noceHex);
console.log('signature:', signature);
console.log('signer:', signer.address);

SignatureVerification.md

This is an example about how to generate a Ethereum signature using Ethers.js functions.

This also includes smart-contract code to verify the signature.

Deployed on Sepolia: 0xd6da38bf53801f1c7707ed2c5f9eba15e80e33ae.

The generated signature is EIP-191 compliant.

SignatureVerification.sol

// SPDX-License-Identifier: AGPL-3.0-or-later
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/utils/cryptography/ECDSA.sol";
import "@openzeppelin/contracts/utils/cryptography/MessageHashUtils.sol";

contract SignatureVerification {
    using ECDSA for bytes32;
    using MessageHashUtils for bytes;

    function verifySignature(
        bytes memory message,
        bytes memory signature,
        address signer
    ) public pure returns (bool) {
        return message.toEthSignedMessageHash().recover(signature) == signer;
    }
}