Signing your APK’s
APK signatures allow developers to identify the author of the application and to update their application without creating complicated interfaces and permissions. Every APK that is run on the Android platform must be signed by the developer. Applications that attempt to install without being signed will be rejected by the package installer on the Android device.
Multiple APK’s can share the same signature.
A Keystore file contains collections of keys, a specified key from a keystore is used to sign and secure Android applications.
Keystore Management
Android Studio
Android studio offers a nice UI for managing keystore files.
Under Build → Generate Signed Bundle / APK → APK
Unity
Under Project Settings → Player → Publishing Settings
It’s worth noting that Unity’s UI does not provide much feedback during keystore management and usage. If you input a password incorrectly, check the Unity console for an error.