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ERC-7913 signature verifier for ZKEmail (#103)
Co-authored-by: ernestognw <ernestognw@gmail.com>
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‎contracts/utils/cryptography/ERC7913SignatureVerifierZKEmail.sol‎

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// SPDX-License-Identifier: MIT
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pragma solidity ^0.8.24;
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import {IDKIMRegistry} from "@zk-email/contracts/DKIMRegistry.sol";
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import {IVerifier} from "@zk-email/email-tx-builder/interfaces/IVerifier.sol";
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import {EmailAuthMsg} from "@zk-email/email-tx-builder/interfaces/IEmailTypes.sol";
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import {IERC7913SignatureVerifier} from "../../interfaces/IERC7913.sol";
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import {ZKEmailUtils} from "./ZKEmailUtils.sol";
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/**
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* @dev ERC-7913 signature verifier that supports ZKEmail accounts.
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*
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* This contract verifies signatures produced through ZKEmail's zero-knowledge
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* proofs which allows users to authenticate using their email addresses.
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*
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* The key decoding logic is customizable: users may override the {_decodeKey} function
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* to enforce restrictions or validation on the decoded values (e.g., requiring a specific
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* verifier, templateId, or registry). To remain compliant with ERC-7913's statelessness,
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* it is recommended to enforce such restrictions using immutable variables only.
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*
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* Example of overriding _decodeKey to enforce a specific verifier, registry, (or templateId):
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*
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* ```solidity
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* function _decodeKey(bytes calldata key) internal view override returns (
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* IDKIMRegistry registry,
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* bytes32 accountSalt,
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* IVerifier verifier,
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* uint256 templateId
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* ) {
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* (registry, accountSalt, verifier, templateId) = super._decodeKey(key);
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* require(verifier == _verifier, "Invalid verifier");
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* require(registry == _registry, "Invalid registry");
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* return (registry, accountSalt, verifier, templateId);
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* }
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* ```
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*/
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abstract contract ERC7913SignatureVerifierZKEmail is IERC7913SignatureVerifier {
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using ZKEmailUtils for EmailAuthMsg;
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/**
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* @dev Verifies a zero-knowledge proof of an email signature validated by a {DKIMRegistry} contract.
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*
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* The key format is ABI-encoded (IDKIMRegistry, bytes32, IVerifier, uint256) where:
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*
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* * IDKIMRegistry: The registry contract that validates DKIM public key hashes
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* * bytes32: The account salt that uniquely identifies the user's email address
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* * IVerifier: The verifier contract instance for ZK proof verification.
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* * uint256: The template ID for the command
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*
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* See {_decodeKey} for the key encoding format.
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*
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* The signature is an ABI-encoded {ZKEmailUtils-EmailAuthMsg} struct containing
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* the command parameters, template ID, and proof details.
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*
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* Signature encoding:
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*
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* ```solidity
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* bytes memory signature = abi.encode(EmailAuthMsg({
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* templateId: 1,
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* commandParams: [hash],
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* proof: {
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* domainName: "example.com", // The domain name of the email sender
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* publicKeyHash: bytes32(0x...), // Hash of the DKIM public key used to sign the email
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* timestamp: block.timestamp, // When the email was sent
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* maskedCommand: "Sign hash", // The command being executed, with sensitive data masked
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* emailNullifier: bytes32(0x...), // Unique identifier for the email to prevent replay attacks
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* accountSalt: bytes32(0x...), // Unique identifier derived from email and account code
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* isCodeExist: true, // Whether the account code exists in the proof
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* proof: bytes(0x...) // The zero-knowledge proof verifying the email's authenticity
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* }
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* }));
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* ```
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*/
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function verify(
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bytes calldata key,
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bytes32 hash,
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bytes calldata signature
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) public view virtual override returns (bytes4) {
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(IDKIMRegistry registry_, bytes32 accountSalt_, IVerifier verifier_, uint256 templateId_) = abi.decode(
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key,
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(IDKIMRegistry, bytes32, IVerifier, uint256)
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);
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EmailAuthMsg memory emailAuthMsg = abi.decode(signature, (EmailAuthMsg));
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return
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(abi.decode(emailAuthMsg.commandParams[0], (bytes32)) == hash &&
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emailAuthMsg.templateId == templateId_ &&
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emailAuthMsg.proof.accountSalt == accountSalt_ &&
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emailAuthMsg.isValidZKEmail(registry_, verifier_) == ZKEmailUtils.EmailProofError.NoError)
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? IERC7913SignatureVerifier.verify.selector
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: bytes4(0xffffffff);
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}
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/**
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* @dev Decodes the key into its components.
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*
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* ```solidity
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* bytes memory key = abi.encode(registry, accountSalt, verifier, templateId);
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* ```
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*/
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function _decodeKey(
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bytes calldata key
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)
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internal
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view
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virtual
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returns (IDKIMRegistry registry, bytes32 accountSalt, IVerifier verifier, uint256 templateId)
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{
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return abi.decode(key, (IDKIMRegistry, bytes32, IVerifier, uint256));
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}
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}

‎contracts/utils/cryptography/SignerZKEmail.sol‎

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return _registry;
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}
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/// @dev An instance of the Verifier contract.
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/// See https://docs.zk.email/architecture/zk-proofs#how-zk-email-uses-zero-knowledge-proofs[ZK Proofs].
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/**
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* @dev An instance of the Verifier contract.
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* See https://docs.zk.email/architecture/zk-proofs#how-zk-email-uses-zero-knowledge-proofs[ZK Proofs].
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*/
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function verifier() public view virtual returns (IVerifier) {
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return _verifier;
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}

‎test/account/AccountERC7913.test.js‎

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@@ -3,7 +3,7 @@ const { loadFixture } = require('@nomicfoundation/hardhat-network-helpers');
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const { getDomain } = require('@openzeppelin/contracts/test/helpers/eip712');
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const { ERC4337Helper } = require('../helpers/erc4337');
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const { NonNativeSigner, P256SigningKey, RSASHA256SigningKey } = require('../helpers/signers');
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const { NonNativeSigner, P256SigningKey, RSASHA256SigningKey, ZKEmailSigningKey } = require('../helpers/signers');
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const { PackedUserOperation } = require('../helpers/eip712-types');
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const { shouldBehaveLikeAccountCore, shouldBehaveLikeAccountHolder } = require('./Account.behavior');
@@ -15,15 +15,36 @@ const signerECDSA = ethers.Wallet.createRandom();
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const signerP256 = new NonNativeSigner(P256SigningKey.random());
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const signerRSA = new NonNativeSigner(RSASHA256SigningKey.random());
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// Constants for ZKEmail
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const accountSalt = '0x046582bce36cdd0a8953b9d40b8f20d58302bacf3bcecffeb6741c98a52725e2'; // keccak256("test@example.com")
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const selector = '12345';
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const domainName = 'gmail.com';
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const publicKeyHash = '0x0ea9c777dc7110e5a9e89b13f0cfc540e3845ba120b2b6dc24024d61488d4788';
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const emailNullifier = '0x00a83fce3d4b1c9ef0f600644c1ecc6c8115b57b1596e0e3295e2c5105fbfd8a';
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const templateId = ethers.solidityPackedKeccak256(['string', 'uint256'], ['TEST', 0n]);
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// Minimal fixture common to the different signer verifiers
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async function fixture() {
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// EOAs and environment
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const [beneficiary, other] = await ethers.getSigners();
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const [admin, beneficiary, other] = await ethers.getSigners();
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const target = await ethers.deployContract('CallReceiverMockExtended');
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// DKIM Registry for ZKEmail
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const dkim = await ethers.deployContract('ECDSAOwnedDKIMRegistry');
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await dkim.initialize(admin, admin);
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await dkim
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.SET_PREFIX()
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.then(prefix => dkim.computeSignedMsg(prefix, domainName, publicKeyHash))
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.then(message => admin.signMessage(message))
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.then(signature => dkim.setDKIMPublicKeyHash(selector, domainName, publicKeyHash, signature));
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// ZKEmail Verifier
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const zkEmailVerifier = await ethers.deployContract('ZKEmailVerifierMock');
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// ERC-7913 verifiers
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const verifierP256 = await ethers.deployContract('ERC7913SignatureVerifierP256');
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const verifierRSA = await ethers.deployContract('ERC7913SignatureVerifierRSA');
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const verifierZKEmail = await ethers.deployContract('$ERC7913SignatureVerifierZKEmail');
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// ERC-4337 env
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const helper = new ERC4337Helper();
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.then(signature => Object.assign(userOp, { signature }));
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};
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return { helper, verifierP256, verifierRSA, domain, target, beneficiary, other, makeMock, signUserOp };
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return {
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helper,
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verifierP256,
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verifierRSA,
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verifierZKEmail,
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dkim,
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zkEmailVerifier,
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domain,
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target,
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beneficiary,
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other,
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makeMock,
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signUserOp,
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};
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}
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describe('AccountERC7913', function () {
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shouldBehaveLikeERC1271({ erc7739: true });
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shouldBehaveLikeERC7821();
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});
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// Using ZKEmail with an ERC-7913 verifier
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describe('ZKEmail', function () {
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beforeEach(async function () {
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// Create ZKEmail signer
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this.signer = new NonNativeSigner(
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new ZKEmailSigningKey(domainName, publicKeyHash, emailNullifier, accountSalt, templateId),
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);
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// Create account with ZKEmail verifier
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this.mock = await this.makeMock(
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ethers.concat([
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this.verifierZKEmail.target,
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ethers.AbiCoder.defaultAbiCoder().encode(
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['address', 'bytes32', 'address', 'uint256'],
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[this.dkim.target, accountSalt, this.zkEmailVerifier.target, templateId],
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),
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]),
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);
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// Override the signUserOp function to use the ZKEmail signer
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this.signUserOp = async userOp => {
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const hash = await userOp.hash();
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return Object.assign(userOp, { signature: this.signer.signingKey.sign(hash).serialized });
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};
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});
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shouldBehaveLikeAccountCore();
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shouldBehaveLikeAccountHolder();
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shouldBehaveLikeERC1271({ erc7739: true });
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shouldBehaveLikeERC7821();
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});
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});

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