1.Symbian charging certificate signature. That is, sign with the official charging certificate issued by Symbian (Saipan) mobile phone operating system. Only the software that has passed the Symbian security certification can obtain the Symbian certificate. This kind of certification needs to be paid, and it may be re-certified every time the version is updated. This kind of software has a high level of security. Can be installed/run normally on the mobile phone/and can realize all the functions provided by the software. 2. The author signed a public certificate. The software author signed the software with a public free certificate when releasing the software. This kind of software can be installed and run on your mobile phone (you may encounter a security warning and you can skip it). However, due to the low authority of the public free certificate, those "special restrictions" functions cannot be realized. If a software doesn't involve this function at all, it is entirely possible for the software author to sign it himself. Another possibility is that although some functions of the software are within the scope of "special restrictions", they are not the main functions. The software author may also release an "author's signature version", which can normally use most functions, but will lose some specific functions. For example, there is such a version of the "incoming call" software that almost all functions can be used, but it can't be started automatically. 3. User signature (using development certificate). Strictly speaking, this should belong to the "developer signature". Because Symbian provides a kind of "development certificate" for software developers, the original intention is to let software developers do software testing. This "development certificate" is associated with the IMEI code of the machine used for testing. The software signed with this certificate can only be used on the machine corresponding to the IMEI code, not on other machines. Our so-called "self-signature" is actually in this way. To put it bluntly, you said you were developing software, you provided the IMEI code of your tester, and Symbian issued you a "development certificate". You use this certificate to sign your Test Software. You are responsible for your "development behavior"! That's all. In addition, the development certificate is valid for three years from the date of issuance, but there is no limit on the use time of the signed program (after the certificate expires, it can be installed by modifying the date of the mobile phone system, and then modified after installation).