A Novel Trusted Software Base for Commercial Android Devices Using Secure TF Card

Table 1

Cases of different modifications and their boot status.

	Bootloader	Kernel	System	TSB	Boot status
Case 1	✗				Boot up
Case 2	✗	✔			Shutdown
Case 3	✗		✔		Shutdown
Case 4	✗			✔	Shutdown

✔ stands for modified content. stands for unchanged content. Since the bootloader of commercial device cannot be modified, it is marked with ✗. It can be seen that any cases that modify any content on the boot chain cannot be successfully started.