Commonly used software generally does not need to be signed, such as qq, Dentsu, ucweb, Reliance Guardian, Tiantianle, etc.

Many other softwares must be signed, such as msn, Pepsi scenes, games and so on.

A mobile phone imei code corresponds to a certificate, because the imei code will not be repeated, you can think that a mobile phone corresponds to a certificate.

The certificate is generally valid for 3 years, but if the certificate is valid for more than 3 years, you can adjust the time back to the previous date and then adjust it back after installation.

As long as the software is installed, there is no time limit, and that certificate is valid only if it is installed.