What is UEFI Secure Boot’s purpose? How does it protect PCs from rootkits & malware?

UEFI Secure Boot’s primary purpose is to enhance computer security by preventing malicious software, especially rootkits, from loading during the critical system startup process. It acts as a vital security mechanism designed to protect modern PCs from unauthorized software and cyber threats that attempt to infect the pre-boot environment before the operating system even has a chance to fully load. This feature ensures that only authentic and trusted software components are executed when a computer powers on, thus safeguarding the integrity of the boot sequence.

To achieve this protection from rootkits and other malware, UEFI Secure Boot operates by verifying the digital signatures of every piece of boot software. This includes the boot loader, operating system kernel, and other firmware components. When a computer with Secure Boot enabled starts, the system’s firmware checks these digital signatures against a database of trusted keys stored within the UEFI firmware. If the software’s signature is valid and matches a trusted key, it is permitted to load and execute. However, if the signature is missing, invalid, or belongs to untrusted or potentially malicious code, UEFI Secure Boot blocks its execution. This prevents stealthy rootkits, which embed themselves deep in the boot process to gain persistent control, from compromising the system at its most fundamental level, ensuring that only authenticated code runs and maintains the computer security of the modern computing environment.