invalid character '\u0081' after top-level value

[GuoxinL]

cocert combine -f cocert0.key -f cocert1.key -o combine.key Loading PEMs from files... (Press Enter to continue without decrypt...) Enter your password for cocert0.key: Enter your password for cocert1.key: Decrypting TUF encrypted PEMs... Enter your master key: unable to decrypt X509 encoded TUF: invalid character '\u0081' after top-level value

What is the "master key" and what should I fill in, my private key is not password