Software signature is the proof of the installation of mobile phone identification software APK, which is a random number generated according to a certain algorithm (such as elliptic algorithm). When installing the software APK, users will judge whether there is software with the same name by the signature carried in the software APK. If it is consistent, it will be cover the installation; If not, the installation will not be possible. At this point, you need to uninstall before installing a new version of the software.

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In the Android platform, the execution file of dalvikvm is encapsulated in apk format, and eventually the runtime loader will decompress it, and then obtain the security access related to the permission branch in the compiled androidmanifest.xml file, but there are still many security restrictions. If the apk file is transferred to the /system/app folder, the execution is unrestricted.

The installed file may not be in this folder, but in androidrom, the apk file of the system will be placed in this folder by default, and it has root permission.