Secure boot is one feature of the Unified Extensible Firmware Interface, or UEFI, the replacement for the BIOS on common hardware devices like PCs and laptops. (This is commonly referred to as the UEFI BIOS and I shall use this term right through this article).
Microsoft has implemented secure boot in a certain manner and since all hardware manufacturers will be following suit, any vendor of an operating system other than Windows has to follow Microsoft's system to get their operating systems to boot on machines on which secure boot is in operation. All devices that come with Windows 8 pre-installed have secure boot turned on.
PC motherboards that sell in retail come with secure boot off. You can turn it on after building your machine. The boards available in Australia at the moment need a UEFI BIOS upgrade before they will support secure boot.
Microsoft controls the key signing authority and has outsourced the job to Verisign; thus any keys purchased have to be bought from Verisign. Each key costs $US99.
On the x86 platform, Microsoft has mandated that there needs to be a way for secure boot to be turned off. This is not due to a sudden bout of kindness; if Microsoft did not do so, then there would probably be another anti-trust lawsuit given the dominance that Microsoft enjoys on this platform. Vendors are thus required to provide a means of turning off secure boot. However, on the ARM platform, there is no requirement for such a mechanism; there is no fear of an anti-trust suit, at least not yet, as no operating system vendor has a near monopoly of the platform.
Linux (the kernel) has been able to boot on UEFI systems for quite some time. But that does not mean a Linux distribution can boot on a system which is locked down using secure boot. And here is where there is much confusion; one of the most confusing documents I found over the last few days is this, where the reader will come away with the impression that UEFI and secure boot are one and the same thing.
The best way to understand the new technology is to get hands-on and that is what I have done: I have installed Windows 8 without secure boot, and then done an install with secure boot turned on. I built a machine with an MSI Z77A-G41 motherboard for these experiments; given that the layout for the UEFI BIOS differs from one major manufacturer to the next, my conclusions are for this hardware only. Your mileage may vary.
Now to Ubuntu. The 64-bit version of the last release of Ubuntu, 12.10, will boot on a machine which has Windows 8 installed with secure boot turned on. But Canonical never made mention of this in its release notes. You can find out by snooping around on mailing lists and reading comments by people who belong to the FOSS community but treat this kind of information like a trade secret.
Getting a medium like a DVD or USB to boot on a system running Windows 8 with secure boot is painful; you have to pop in your Ubuntu DVD while either within the system or at the start-up screen, move your mouse to the lower right-hand corner of the screen, click on Settings and then on the power icon (from within Windows) or on the power button (at the start-up screen - above). Then hold down the shift key and click on Restart. You will then get a choice of choosing a device to boot from. After that you will have to go through at least one restart; repeat the process of shift-clicking and you will finally be presented with a screen where you can choose your DVD drive. Ubuntu will then boot.
But you cannot install Ubuntu 12.10 64-bit on a Windows 8 secure boot machine which has a single hard drive. This is the screen (above) that greets you soon after you begin the installation procedure. Ubuntu cannot recognise the fact that Windows 8 is installed on this system.
Ubuntu has a method of installing from within Windows; I tried this on the same system (Windows 8 with secure boot) but though the install ran to completion, and I was presented with a choice of operating systems to boot from (above), Ubuntu would not boot (below).
I then added a second drive to my PC and went through the Ubuntu installation procedure manually. I was able to install Ubuntu on the second drive. But there is no choice of operating systems presented at boot-time; I have to go through the shift-click process I outlined above and then I can choose to boot into the drive running Ubuntu. For some strange reason, I get two icons named Ubuntu (below). Only the lower one works, though.
No other Linux distribution that I know of has implemented the ability to boot on a machine that has Windows 8 running with secure boot turned on. The recent beta of Fedora 18 cannot; Anna Eusebio of Red Hat confirmed this to iTWire. Once again, it would have been child's play to make mention of this in the release notes. But no, instead one has to go through a week of waiting to hear from a PR person. Nobody knows how to do media like people in free and open source software; they are a class apart.
The latest version of openSUSE, 12.2, does not support secure boot either; the next release is expected to offer full support.
As to the people involved in working on getting various Linux distributions to the stage where they can support secure boot, I have a word of advice: continue to post the information you have in your own secret corner of the web. Don't, just don't, issue it to the wider public. You never know, you just might get too many people starting to experiment with using GNU/Linux. And that would mean that it isn't an exclusive club any more.