If you are too lazy to apply, download the fee deduction buster to your mobile phone, enter the network management, download the network monitoring plug-in, and the key and cer file will be automatically downloaded to your /system/cert folder in less than 2 minutes.

Download the free signature, sign on the computer and install it in the mobile phone. Software with certificate errors in the future can be signed with free signature before installation.

The format doesn't support risk or anything. Don't worry, just keep pretending.

Nokia basically supports sis and jar files.