While booting the TPM-based key was used to check the key and the measurements details are correct. During the Boot Process of a system, During the boot process of a system the boot code including firmware and the OS components are loaded and recorded in the TPM, these recording is known as measurements and that can be used as evidence to boot a system only when correct software was used. The most commonly used TPM functions are for system integrity measurements and for key creation and use.
