The reference implementation of an MBA factory contract is available at https://eips.ethereum.org/EIPS/eip-6551#registry.

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Account Interface

The MBA implementation should follow the rules as described below:
  • All token bound accounts SHOULD be created via the singleton registry;
  • All token bound account implementations MUST implement ERC-165 interface detection;
  • All token bound account implementations MUST implement ERC-1271 signature validation.
  • All token bound account implementations MUST implement the following interface.
/// @dev the ERC-165 identifier for this interface is `0x6faff5f1`
interface IERC6551Account {
     /**
      * @dev Allows the account to receive Ether.
      *
      * Accounts MUST implement a `receive` function.
      *
      * Accounts MAY perform arbitrary logic to restrict conditions
      * under which Ether can be received.
      */
     receive() external payable;
     /**
      * @dev Returns the identifier of the non-fungible token which owns the account.
      *
      * The return value of this function MUST be constant - it MUST NOT change over time.
      *
      * @return chainId       The chain ID of the chain the token exists on
      * @return tokenContract The contract address of the token
      * @return tokenId       The ID of the token
      */
     function token() external view returns (uint256 chainId, address tokenContract, uint256 tokenId);
     /**
      * @dev Returns a value that SHOULD be modified each time the account changes state.
      *
      * @return The current account state
      */
     function state() external view returns (uint256);
     /**
      * @dev Returns a magic value indicating whether a given signer is authorized to act on behalf
      * of the account.
      *
      * MUST return the bytes4 magic value 0x523e3260 if the given signer is valid.
      *
      * By default, the holder of the non-fungible token the account is bound to MUST be considered
      * a valid signer.
      *
      * Accounts MAY implement additional authorization logic which invalidates the holder as a
      * signer or grants signing permissions to other non-holder accounts.
      *
      * @param  signer     The address to check signing authorization for
      * @param  context    Additional data used to determine whether the signer is valid
      * @return magicValue Magic value indicating whether the signer is valid
      */
     function isValidSigner(address signer, bytes calldata context)
         external
         view
         returns (bytes4 magicValue);
}