The KEY of the enterprise side of the online certification system is a key.dat file exported by the Internal Revenue Service server. When the file is lost, you can contact [enterprise administrator] or [online certification software service provider], and they can export a new key.dat file from the national tax side to you. Or go directly to the IRS hall, apply for a KEY.DAT file (USB flash drive or computer copy) If it is new, take the application form to your national tax bureau to copy the USB flash drive. If the old household, take the payment receipt to take the U disk to your national tax branch to copy.