Cracking the phone is equivalent to getting the highest authority. Generally, a Nokia mobile phone is called cracking, which is equivalent to the ROOT of Android and the jailbreak of iphone. I think your mobile phone belongs to Nokia, so you don't need to sign it after cracking it. Simply put, it is a certificate. In order to ensure the security of the system, all software installed in Nokia mobile phones need a certificate, which is equivalent to a legal installation license, before this software can be installed in mobile phones. Generally, software that needs to be signed will prompt a certificate error during installation. Of course, there is also the possibility of a certificate error, that is, there is no certificate. At this time, you need to apply. When I encounter a certificate error, I first think of the need to sign, and go to Skynet or Lexun to sign a software called Saipan Direct. After installation, the operation is very simple, so I won't talk about it. If you still prompt that the certificate error is no certificate after signing, you can apply to Lexun.