Hello ERC20 Permit

npm i

# Test signature verification(generate Hash onchain)
npx hardhat test test/verify-signature.js

# Test signature2 verification(generate Hash offchain)
npx hardhat test test/verify-signature2.js

# Test ERC20 Permit
npx hardhat test test/erc20-permit.js

Links

1. https://docs.ethers.io/v5/api/signer/#Signer-signMessage

2. https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/extensions/draft-IERC20Permit.sol

3. https://github.com/Uniswap/v3-periphery/blob/main/test/shared/permit.ts

Related EIP

1. EIP-712: Typed structured data hashing and signing
2. EIP-2612: permit – 712-signed approvals
3. https://eips.ethereum.org/EIPS/eip-191

structure

stage	details	ethers.js
initial	encode(Tx: T) = RLP_encode(Tx)
normal	encode(message) = "\x19Ethereum Signed Message:\n" || len(message)||message	signer.sigMessage(hash)
EIP-712	encode(domainSeparator, message) = "\x19\x01"||domainSeparator||hashStruct(message)	signer._signTypeData()
EIP-2612	special case for EIP-712