For the uninitiated, some months ago, Microsoft announced that all PCs that were certified as capable of running Windows 8 would include the Unified Extensible Firmware Interface. This means that booting would be regulated by means of keys, ostensibly to ensure that no malware can operate at that level.
Red Hat's method of ensuring that such PCs can boot GNU/Linux, announced by its community distribution Fedora, is to sign up to the Microsoft developer program and obtain a key which will be used to sign a "shim" bootloader. This shim would then load the GRUB2 bootloader which will boot the operating system kernel. As the key comes from Microsoft, it will be recognised by most PCs and laptops.
On the x86 platform, there is the option of turning off this regulated boot process which is being called, rather fatuously, secure boot. This came about due to opposition from other companies. But on the ARM platform, secure boot is mandated by Microsoft and there are no exceptions. You pays your money, but you have no choice.
Ubuntu's plan involves having a key which is distribution-specific in the firmware, and also a key vouched for by Microsoft. CDs which are sold or distributed separately from hardware will need Microsoft's key to be present in the firmware to boot while bootloader images from the Canonical website will have Ubuntu's own key.