LTE devices use a secure boot process that consists of several stages, each of which checks the signature and key of the next stage before allowing it to execute. The first stage is the boot ROM, which is a small and fixed program that is stored in a read-only memory chip inside the device. The boot ROM contains the public key of the device manufacturer, which it uses to verify the second stage, the boot loader. The boot loader is a larger program that is stored in a flash memory chip inside the device. The boot loader contains the public key of the network operator, which it uses to verify the third stage, the firmware. The firmware is the software that controls the radio and the hardware components of the device. The firmware contains the public key of the operating system, which it uses to verify the fourth stage, the kernel. The kernel is the core of the operating system, which manages the resources and processes of the device. The kernel contains the public key of the applications, which it uses to verify the fifth stage, the user interface and the apps. The user interface and the apps are the software that provides the features and functionalities of the device to the user.