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When Secure Boot is enabled, it is initially placed in "setup" mode, which allows a public key known as the "platform key" (PK) to be written to the firmware. Once the key is written, Secure Boot enters "User" mode, where only UEFI drivers and OS boot loaders signed with the platform key can be loaded by the firmware.
Pre-boot authentication (PBA) or power-on authentication (POA) [1] serves as an extension of the BIOS, UEFI or boot firmware and guarantees a secure, tamper-proof environment external to the operating system as a trusted authentication layer.
A Trusted Platform Module (TPM) is a secure cryptoprocessor that implements the ISO/IEC 11889 standard. Common uses are verifying that the boot process starts from a trusted combination of hardware and software and storing disk encryption keys. A TPM 2.0 implementation is part of the Windows 11 system requirements. [1]
If UEFI Secure Boot is supported, a "shim" or "Preloader" is often booted by the UEFI before the bootloader or EFI-stub-bearing kernel. [11] Even if UEFI Secure Boot is disabled this may be present and booted in case it is later enabled. It merely acts to add an extra signing key database providing keys for signature verification of subsequent ...
You can disable Secure Boot by restarting your PC and opening the Unified Extensible Firmware Interface (UEFI).
Prior to the development and ubiquitous adoption of the Plug and Play BIOS standard, an add-on device such as a hard disk controller or a network adapter card (NIC) was generally required to include an option ROM in order to be bootable, as the motherboard BIOS did not include any support for the device and so could not incorporate it into the BIOS's boot protocol.
When interrupt 19h is called, the BIOS attempts to locate boot loader software on a "boot device", such as a hard disk, a floppy disk, CD, or DVD. It loads and executes the first boot software it finds, giving it control of the PC. [28] The BIOS uses the boot devices set in Nonvolatile BIOS memory , or, in the earliest PCs, DIP switches.
The ACM then measures the first BIOS code module, which can make additional measurements. The measurements of the ACM and BIOS code modules are extended to PCR0, which is said to hold the static core root of trust measurement (CRTM) as well as the measurement of the BIOS Trusted Computing Base (TCB). The BIOS measures additional components into ...