Since smart contract accounts don’t have a way to validate signatures like an EOA, it is also recommended that you implement EIP-1271 for your smart contract accounts. This EIP provides a standardized way for smart contracts to verify whether a signature is valid for a given message.

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EIP-1271 Specification

EIP-1271 specifies a single function, isValidSignature, that can contain any arbitrary logic to validate a given signature and largely depends on how you have implemented your smart contract account. 
contract ERC1271 {

  // bytes4(keccak256("isValidSignature(bytes32,bytes)"))
  bytes4 constant internal MAGICVALUE = 0x1626ba7e;

  /**
   * @dev Should return whether the signature provided is valid for the provided hash
   * @param _hash      Hash of the data to be signed
   * @param _signature Signature byte array associated with _hash
   *
   * MUST return the bytes4 magic value 0x1626ba7e when function passes.
   * MUST NOT modify state (using STATICCALL for solc < 0.5, view modifier for solc > 0.5)
   * MUST allow external calls
   */ 
  function isValidSignature(
    bytes32 _hash, 
    bytes memory _signature)
    public
    view 
    returns (bytes4 magicValue);
}

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OpenZeppelin Implementation

OpenZeppelin provides a way to verify signatures for different account implementations that you can use in your smart contract account. Install the OpenZeppelin contracts library: 
npm install @openzeppelin/contracts
Implement the isValidSignature function in your smart contract account: 
import {IAccount, ACCOUNT_VALIDATION_SUCCESS_MAGIC} from "./interfaces/IAccount.sol";
import { SignatureChecker } from "@openzeppelin/contracts/utils/cryptography/SignatureChecker.sol";

contract MyAccount is IAccount {
    using SignatureChecker for address;

    function isValidSignature(
        address _address,
        bytes32 _hash,
        bytes memory _signature
    ) public pure returns (bool) {
        return _address.isValidSignatureNow(_hash, _signature);
    }
}

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Verifying Signatures

On the client, you can use zksync-ethers to verify signatures for your smart contract account using either:
  • isMessageSignatureCorrect for verifying a message signature.
  • isTypedDataSignatureCorrect for verifying a typed data signature.
export async function isMessageSignatureCorrect(address: string, message: ethers.Bytes | string, signature: SignatureLike): Promise<boolean>;

export async function isTypedDataSignatureCorrect(
  address: string,
  domain: TypedDataDomain,
  types: Record<string, Array<TypedDataField>>,
  value: Record<string, any>,
  signature: SignatureLike
): Promise<boolean>;
Both of these methods return true or false depending on whether the message signature is correct. Currently, these methods only support verifying ECDSA signatures, but will soon also support EIP-1271 signature verification.