Hackers GliGli & Tiros developed a Hack which glitches all recent Xbox 360 Kernels to run unsigned code on.
This means it's now possible to run homebrew & backups on all Xbox 360s, no matter which firmware is loaded, in the past this was only possible on Xbox 360s with a certain firmware-level. This also opens the possibility to run quite easily Linux on your Xbox 360!
Although this is quite an easy hack, it requires some hardware modifications.
Here's an extract of the tutorial:
Software based approaches of running unsigned code on the 360 mostly don't work, it was designed to be secure from a software point of view.
The processor starts running code from ROM (1bl) , which then starts loading a RSA signed and RC4 crypted piece of code from NAND (CB).
CB then initialises the processor security engine, its task will be to do real time encryption and hash check of physical DRAM memory. From what we found, it's using AES128 for crypto and strong (Toeplitz ?) hashing. The crypto is different each boot because it is seeded at least from:
- A hash of the entire fuseset.
- The timebase counter value.
- A truly random value that comes from the hardware random number generator the processor embeds. on fats, that RNG could be electronically deactivated, but there's a check for "apparent randomness" (merely a count of 1 bits) in CB, it just waits for a seemingly proper random number.
CB can then run some kind of simple bytecode based software engine whose task will mainly be to initialise DRAM, CB can then load the next bootloader (CD) from NAND into it, and run it.
Basically, CD will load a base kernel from NAND, patch it and run it.
That kernel contains a small privileged piece of code (hypervisor), when the console runs, this is the only code that would have enough rights to run unsigned code.
In kernel versions 4532/4548, a critical flaw in it appeared, and all known 360 hacks needed to run one of those kernels and exploit that flaw to run unsigned code.
On current 360s, CD contains a hash of those 2 kernels and will stop the boot process if you try to load them.
The hypervisor is a relatively small piece of code to check for flaws and apparently no newer ones has any flaws that could allow running unsigned code.
On the other hand, tmbinc said the 360 wasn't designed to withstand certain hardware attacks such as the timing attack and "glitching".
Glitching here is basically the process of triggering processor bugs by electronical means.
This is the way we used to be able to run unsigned code.
You can read the whole thread on the Libxenon forum here, about this hack.
You can watch a video of this hack here.