Every smart phone has its own serial number, and the certificate is made with this serial number, so everyone's certificate is different. You press *#06# and your own serial number will appear. Tell the person who gave you this serial number and you will get a certificate of your own. Intelligent machine belongs to S60 system, and other machines are generally S40 system. Generally, S40 can only install software in jar format, and S60 can install software in jar format, sis format and SIXX format. Some software in sis and SIXX formats can only be installed after you sign it. For example, the software for changing fonts on mobile phones can only be installed after you sign it. You can download a signature software online. You will be prompted when you use it in the future. Please import your certificate. Please select the software you want to sign. Please select the saving method after signing. Signed software can be installed on your mobile phone. Many people like to install software that needs to be signed. Although it is troublesome, it is very safe! Signing with a certificate is mainly for security!