What is a "certificate"? Simply put, a certificate is a passport. Just like a room card, you have to insert the door to open it. Similarly, you use your serial number certificate to sign the software you want to put into your mobile phone. The software cannot be loaded into your mobile phone until it is signed. It's unique, just like a room card. You can't open other doors. (This of course refers to the software that needs to be signed. Many software can be installed without signature, which is not included. When you download the certificate that belongs to your serial number (serial number), first make sure it doesn't need to be installed on your computer or mobile phone. But you must take good care of it. Never put it in a place that can't be found or deleted by mistake, because the current certificate is extremely precious. Valid for 3 years, you can make several copies and put them away. If you need to do it, send me your mobile phone serial number and email address, and I'll do it for you.