Steven Sinofsky explains the UEFI Secure Boot process in Windows 8

There have been some comments about how Microsoft implemented secure boot and unfortunately these seemed to synthesize scenarios that are not the case so we are going to use this post as a chance to further describe how UEFI enables secure boot and the options available to PC manufacturers. The most important thing to understand is that we are introducing capabilities that provide a no-compromise approach to security to customers that seek this out while at the same time full and complete control over the PC continues to be available. Tony Mangefeste on our Ecosystem team authored this post.

  Windows 8: Protecting the pre-OS environment with UEFI