Platform certificate" in rooted android phone

How is posibble get platform certific开发者_JAVA百科ate in rooted android phone. I need to sign an application that makes use of android: sharedUserId = "android.uid.phone".

Someone can help me. thank you very much

Getting the platform certificate has nothing to do with whether the phone is rooted or not.
The platform certificate is created by the manufacturer of the device while signing the firmware. If you are working with the manufacturer, then ask them for it.
Else if your best bet is to compile the OS for your phone yourself, sign it with your own keys and use the same keys to sign the application's apk.