How to use compact signatures with EIP2098

[rahulrumalla]

Hi. I'm having trouble figuring out the right way to construct the argument using ethers.js for a contract that's using EIP2098

import {SignatureChecker} from "@openzeppelin/contracts/utils/cryptography/SignatureChecker.sol";

function methodWith2098Signature(
  address from,
  string calldata uri,
  bytes calldata signature
) external virtual returns (uint256) {
  ...
  require(SignatureChecker.isValidSignatureNow(from, hash, signature), "invalid signature");
  ...
}

I'm using foundry and in my solidity unit tests, I'm able to call via the following. Sharing the following for reference on how the signature is constructed in the test

(uint8 v, bytes32 r, bytes32 s) = vm.sign(fromPrivateKey, hash);
bytes memory signature = abi.encodePacked(r, s, v);
x.methodWith2098Signature(from, uri, signature); 

On the front-end using ethers, I am accessing the individual params of the signature to prepare the call to contract

const signature = await untypedSigner._signTypedData(domain, TYPES, value);
const { v, r, s, compact, yParityAndS, _vs } = splitSignature(signature);
...
const contract = new Contract(CONTRACT_ADDRESS, MyContract.abi, signer);
await contract['methodWith2098Signature'](fromAddress, "ipfs://some_uri", signature.compact);

I'm wondering what would be right signature param I need to use to call the contract with, is it yParityAndS or compact or?
And would I need to encode this in a different way as the signature parameter on the function is bytes?

Currently, the call is failing when using either the compact or yParityAndS field. It could be something missed on the hash itself, but I wanted to check here if there was something obvious that I was doing wrong.

Thanks 🙏

[rahulrumalla]

UPDATE: It was a configuration error. You can ignore this.

[TimDaub]

@ricmoo Why does

const { compact } = splitSignature(signature);

equal to

(uint8 v, bytes32 r, bytes32 s) = vm.sign(fromPrivateKey, hash);
bytes memory signature = abi.encodePacked(r, s);

and not:

(uint8 v, bytes32 r, bytes32 s) = vm.sign(fromPrivateKey, hash);
bytes memory signature = abi.encodePacked(r, s, v);

[zemse]

compact does not always equal to abi.encodePacked(r, s). It's only if v = 27, however if v = 28 then left-most bit of s has to be flipped to 1.

[alfheimrShiven]

Hey @rahulrumalla I'm trying to use Openzeppelin's ECDSA.sol contract's function recover( bytes32 hash, bytes memory signature) in a unit test written in Foundry.
My test looks exactly like yours in terms of signature creation:

(address signer, uint256 signerPK) = makeAddrAndKey("signer");
(uint8 v, bytes32 r, bytes32 s) = vm.sign(signerPK, hash);
bytes memory signature = abi.encodePacked(v, r, s);

address recoveredSigner = ECDSA.recover(hash, signature); 
assertEq(recoveredSigner, signer);

but I get the error

VM::sign(<pk>, 0x46a4a6b86560880572154cc245188597806bacb2ed65aa43fdd0c670c5f762dc) [staticcall]
    │   └─ ← 27, 0x1b5ae0bf91052a8ac3cfbc285fb915cca056865a1db7b832b851e2907107540b, 0x01a519d1066a48c2f4e43fb12f35144065c7dc82ee057f284502d34908703ca5
    └─ ← "ECDSA: invalid signature 'v' value"

Since you've solved this, just wanted to check if you could help here.

I'm discussing this on another thread with Openzeppelin as well. Thread link.

Let me know :)

[ricmoo]

The v expected by the EVM must be normalized to the value 27 (0x1b) or 28 (0x1c); my guess is you are using a v outside this range, either due to EIP-155 signing (which encodes the chain ID into the v) or EIP-2718 signing (which encodes v as 0 or 1).

This cookbook might help if you are looking for various ways to encode and decode the signature in either JavaScript or Solidity. :)

[alfheimrShiven]

@ricmoo thanks for sharing the resource. Actually, the order in which I was concatenating the v, r, s value was wrong.

(address signer, uint256 signerPK) = makeAddrAndKey("signer");
(uint8 v, bytes32 r, bytes32 s) = vm.sign(signerPK, hash);
bytes memory signature = abi.encodePacked(r, s, v); // note the order

address recoveredSigner = ECDSA.recover(hash, signature);  // works!
assertEq(recoveredSigner, signer);

[Cryptobullyo]

can any one help me
finding unit8 v, Bytes 32r , bytes 32 s
i am trying to pull LP uniswap v2 without using uniswap web interferences.
using ehterscan.io
https://etherscan.io/address/0x7a250d5630b4cf539739df2c5dacb4c659f2488d#writeContract
thanks

function removeLiquidityETHWithPermit(
address token,
uint liquidity,
uint amountTokenMin,
uint amountETHMin,
address to,
uint deadline,
bool approveMax, uint8 v, bytes32 r, bytes32 s
) external returns (uint amountToken, uint amountETH);