Signature Protection Level - Clarification

Question

Since I am new to Android, I wanted to ask something that is not enough for me. I read the API guide about permissions as much more Q & As I look at this topic, I'm still not sure if I understand this correctly. Thus, the level of protection of signatures:

The permission granted by the system only if the requesting application is signed with the same certificate as the application, the declared permission. If the certificates match, the system automatically grants permission without notifying the user or requesting explicit approval of the user.

Does this mean that I can’t use any permission with a signature protection level, so all permissions defined in the Android API and having this level of protection are not available to everyone except the team that is developing it?

Answer 1

Does this mean that I can’t use any permission with a signature protection level, so all permissions defined in the Android API and having this level of protection are not available to everyone except the team that is developing it?

Generally speaking, yes.

In particular, the signature -level permission means that the application protects itself with this permission (for example, through the android:permission attributes), and the application tries to talk to the first application that needs permission (the <uses-permission> element) must be signed by one and the same same signature key.

If the application protecting itself is part of the firmware of the device or the OS itself, only applications signed with the same signature key, since this firmware can talk to the protecting application, while holding this permission.

However, if you write application A that protects itself with signature permission (for example, user-defined), and you write application B that wants to talk to the protected parts of application A, you can do this if you sign applications A and application B with using the same signature key.