Android : Difference between LOCAL_CERTIFICATE values in Android.mk

What is the difference between the different values of the variable LOCAL_CERTIFICATE ?

I know of two values platform and shared. What are the other possible values in Android build system ? How does it effect our application's behaviour.

LOCAL_PATH:= $(call my-dir) include $(CLEAR_VARS)

LOCAL_MODULE_TAGS := optional

LOCAL_SRC_FILES := $(call all-java-files-under, src)

LOCAL_PACKAGE_NAME := abc LOCAL_CERTIFICATE := shared

LOCAL_JNI_STATIC_LIBRARIES := abc

LOCAL_PROGUARD_ENABLED := disabled

include $(BUILD_PACKAGE)

include $(call all-makefiles-under,$(LOCAL_PATH))