Stealth Meta-Address Registry

// SPDX-License-Identifier: CC0-1.0
pragma solidity 0.8.23;

/// @notice `ERC6538Registry` contract to map accounts to their stealth meta-address. See
/// [ERC-6538](https://eips.ethereum.org/EIPS/eip-6538) to learn more.
contract ERC6538Registry {
  /// @notice Emitted when an invalid signature is provided to `registerKeysOnBehalf`.
  error ERC6538Registry__InvalidSignature();

  /// @notice Next nonce expected from `user` to use when signing for `registerKeysOnBehalf`.
  /// @dev `registrant` may be a standard 160-bit address or any other identifier.
  /// @dev `schemeId` is an integer identifier for the stealth address scheme.
  mapping(address registrant => mapping(uint256 schemeId => bytes)) public stealthMetaAddressOf;

  /// @notice A nonce used to ensure a signature can only be used once.
  /// @dev `registrant` is the user address.
  /// @dev `nonce` will be incremented after each valid `registerKeysOnBehalf` call.
  mapping(address registrant => uint256) public nonceOf;

  /// @notice The EIP-712 type hash used in `registerKeysOnBehalf`.
  bytes32 public constant ERC6538REGISTRY_ENTRY_TYPE_HASH =
    keccak256("Erc6538RegistryEntry(uint256 schemeId,bytes stealthMetaAddress,uint256 nonce)");

  /// @notice The chain ID where this contract is initially deployed.
  uint256 internal immutable INITIAL_CHAIN_ID;

  /// @notice The domain separator used in this contract.
  bytes32 internal immutable INITIAL_DOMAIN_SEPARATOR;

  /// @notice Emitted when a registrant updates their stealth meta-address.
  /// @param registrant The account that registered the stealth meta-address.
  /// @param schemeId Identifier corresponding to the applied stealth address scheme, e.g. 1 for
  /// secp256k1, as specified in ERC-5564.
  /// @param stealthMetaAddress The stealth meta-address.
  /// [ERC-5564](https://eips.ethereum.org/EIPS/eip-5564) bases the format for stealth
  /// meta-addresses on [ERC-3770](https://eips.ethereum.org/EIPS/eip-3770) and specifies them as:
  ///   st:<shortName>:0x<spendingPubKey>:<viewingPubKey>
  /// The chain (`shortName`) is implicit based on the chain the `ERC6538Registry` is deployed on,
  /// therefore this `stealthMetaAddress` is just the compressed `spendingPubKey` and
  /// `viewingPubKey` concatenated.
  event StealthMetaAddressSet(
    address indexed registrant, uint256 indexed schemeId, bytes stealthMetaAddress
  );

  /// @notice Emitted when a registrant increments their nonce.
  /// @param registrant The account that incremented the nonce.
  /// @param newNonce The new nonce value.
  event NonceIncremented(address indexed registrant, uint256 newNonce);

  constructor() {
    INITIAL_CHAIN_ID = block.chainid;
    INITIAL_DOMAIN_SEPARATOR = _computeDomainSeparator();
  }

  /// @notice Sets the caller's stealth meta-address for the given scheme ID.
  /// @param schemeId Identifier corresponding to the applied stealth address scheme, e.g. 1 for
  /// secp256k1, as specified in ERC-5564.
  /// @param stealthMetaAddress The stealth meta-address to register.
  function registerKeys(uint256 schemeId, bytes calldata stealthMetaAddress) external {
    stealthMetaAddressOf[msg.sender][schemeId] = stealthMetaAddress;
    emit StealthMetaAddressSet(msg.sender, schemeId, stealthMetaAddress);
  }

  /// @notice Sets the `registrant`'s stealth meta-address for the given scheme ID.
  /// @param registrant Address of the registrant.
  /// @param schemeId Identifier corresponding to the applied stealth address scheme, e.g. 1 for
  /// secp256k1, as specified in ERC-5564.
  /// @param signature A signature from the `registrant` authorizing the registration.
  /// @param stealthMetaAddress The stealth meta-address to register.
  /// @dev Supports both EOA signatures and EIP-1271 signatures.
  /// @dev Reverts if the signature is invalid.
  function registerKeysOnBehalf(
    address registrant,
    uint256 schemeId,
    bytes memory signature,
    bytes calldata stealthMetaAddress
  ) external {
    bytes32 dataHash;
    address recoveredAddress;

    unchecked {
      dataHash = keccak256(
        abi.encodePacked(
          "\x19\x01",
          DOMAIN_SEPARATOR(),
          keccak256(
            abi.encode(
              ERC6538REGISTRY_ENTRY_TYPE_HASH,
              schemeId,
              keccak256(stealthMetaAddress),
              nonceOf[registrant]++
            )
          )
        )
      );
    }

    if (signature.length == 65) {
      bytes32 r;
      bytes32 s;
      uint8 v;
      assembly ("memory-safe") {
        r := mload(add(signature, 0x20))
        s := mload(add(signature, 0x40))
        v := byte(0, mload(add(signature, 0x60)))
      }
      recoveredAddress = ecrecover(dataHash, v, r, s);
    }

    if (
      (
        (recoveredAddress == address(0) || recoveredAddress != registrant)
          && (
            IERC1271(registrant).isValidSignature(dataHash, signature)
              != IERC1271.isValidSignature.selector
          )
      )
    ) revert ERC6538Registry__InvalidSignature();

    stealthMetaAddressOf[registrant][schemeId] = stealthMetaAddress;
    emit StealthMetaAddressSet(registrant, schemeId, stealthMetaAddress);
  }

  /// @notice Increments the nonce of the sender to invalidate existing signatures.
  function incrementNonce() external {
    unchecked {
      nonceOf[msg.sender]++;
    }
    emit NonceIncremented(msg.sender, nonceOf[msg.sender]);
  }

  /// @notice Returns the domain separator used in this contract.
  /// @dev The domain separator is re-computed if there's a chain fork.
  function DOMAIN_SEPARATOR() public view returns (bytes32) {
    return block.chainid == INITIAL_CHAIN_ID ? INITIAL_DOMAIN_SEPARATOR : _computeDomainSeparator();
  }

  /// @notice Computes the domain separator for this contract.
  function _computeDomainSeparator() internal view returns (bytes32) {
    return keccak256(
      abi.encode(
        keccak256(
          "EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"
        ),
        keccak256("ERC6538Registry"),
        keccak256("1.0"),
        block.chainid,
        address(this)
      )
    );
  }
}

/// @notice Interface of the ERC1271 standard signature validation method for contracts as defined
/// in https://eips.ethereum.org/EIPS/eip-1271[ERC-1271].
interface IERC1271 {
  /// @notice Should return whether the signature provided is valid for the provided data
  /// @param hash Hash of the data to be signed
  /// @param signature Signature byte array associated with _data
  function isValidSignature(bytes32 hash, bytes memory signature)
    external
    view
    returns (bytes4 magicValue);
}

// SPDX-License-Identifier: CC0-1.0
pragma solidity 0.8.23;

/// @dev Interface for calling the `ERC6538Registry` contract to map accounts to their stealth
/// meta-address. See [ERC-6538](https://eips.ethereum.org/EIPS/eip-6538) to learn more.
interface IERC6538Registry {
  /// @notice Emitted when an invalid signature is provided to `registerKeysOnBehalf`.
  error ERC6538Registry__InvalidSignature();

  /// @dev Emitted when a registrant updates their stealth meta-address.
  /// @param registrant The account that registered the stealth meta-address.
  /// @param schemeId Identifier corresponding to the applied stealth address scheme, e.g. 1 for
  /// secp256k1, as specified in ERC-5564.
  /// @param stealthMetaAddress The stealth meta-address.
  /// [ERC-5564](https://eips.ethereum.org/EIPS/eip-5564) bases the format for stealth
  /// meta-addresses on [ERC-3770](https://eips.ethereum.org/EIPS/eip-3770) and specifies them as:
  ///   st:<shortName>:0x<spendingPubKey>:<viewingPubKey>
  /// The chain (`shortName`) is implicit based on the chain the `ERC6538Registry` is deployed on,
  /// therefore this `stealthMetaAddress` is just the `spendingPubKey` and `viewingPubKey`
  /// concatenated.
  event StealthMetaAddressSet(
    address indexed registrant, uint256 indexed schemeId, bytes stealthMetaAddress
  );

  /// @notice Emitted when a registrant increments their nonce.
  /// @param registrant The account that incremented the nonce.
  /// @param newNonce The new nonce value.
  event NonceIncremented(address indexed registrant, uint256 newNonce);

  /// @notice Sets the caller's stealth meta-address for the given scheme ID.
  /// @param schemeId Identifier corresponding to the applied stealth address scheme, e.g. 1 for
  /// secp256k1, as specified in ERC-5564.
  /// @param stealthMetaAddress The stealth meta-address to register.
  function registerKeys(uint256 schemeId, bytes calldata stealthMetaAddress) external;

  /// @notice Sets the `registrant`'s stealth meta-address for the given scheme ID.
  /// @param registrant Address of the registrant.
  /// @param schemeId Identifier corresponding to the applied stealth address scheme, e.g. 1 for
  /// secp256k1, as specified in ERC-5564.
  /// @param signature A signature from the `registrant` authorizing the registration.
  /// @param stealthMetaAddress The stealth meta-address to register.
  /// @dev Supports both EOA signatures and EIP-1271 signatures.
  /// @dev Reverts if the signature is invalid.
  function registerKeysOnBehalf(
    address registrant,
    uint256 schemeId,
    bytes memory signature,
    bytes calldata stealthMetaAddress
  ) external;

  /// @notice Increments the nonce of the sender to invalidate existing signatures.
  function incrementNonce() external;

  /// @notice Returns the domain separator used in this contract.
  function DOMAIN_SEPARATOR() external view returns (bytes32);

  /// @notice Returns the stealth meta-address for the given `registrant` and `schemeId`.
  function stealthMetaAddressOf(address registrant, uint256 schemeId)
    external
    view
    returns (bytes memory);

  /// @notice Returns the EIP-712 type hash used in `registerKeysOnBehalf`.
  function ERC6538REGISTRY_ENTRY_TYPE_HASH() external view returns (bytes32);

  /// @notice Returns the nonce of the given `registrant`.
  function nonceOf(address registrant) external view returns (uint256);
}