One of the differentiating factors of Android is the way Android applications are signed. All applications in Android are self-signed. There is no requirement to sign the applications using a certificate authority. This is different from traditional application signing where a signature identifies the author and bases trust upon the signature.
The signature of the application associates the app with the author. If a user installs multiple applications written by the same author and these applications want to share each other's data, they need to be associated with the same signature and should have a
SHARED_ID flag set in the manifest file.
The application signature is also used during the application upgrade. An application ...