Simply put, a certificate is an installation license. With it, you can sign the software you want to install, and the signed software can be installed in your mobile phone. You can try to move the mobile phone forward for half a year, and then switch back to S60, the third edition, which greatly improves the security and has stricter regulations on the third-party software installed and running in the system. Some operations involving mobile phone software and hardware security/personal information security are particularly restricted (for example, automatic startup of mobile phone startup is one of the restricted functions). In order to realize these "specially restricted" functions, the application must obtain a "signature". In other words, someone should be responsible for the safety of this operation! A program without any signature cannot be installed and run.