Just wanted to explain to you all the basic concept of the boot process of a 360.

From power-on:
1. 1BL (first bootloader, stored in CPU ROM), this loads decrypts and starts:
2. CB (2BL, 2nd bootloader, stored in NAND), this this loads decrypts and starts:
3. CD. This loads, decrypts and decompresses CE, which contains the base kernel + base HV (Hypervisor). It also loads decrypts and then starts:
4. CF. This loads, decrypts and decompresses CG, which contains the patches for kernel and HV. It then applies the patches and starts up the patched HV and then the patched kernel. Then it boots to the dashboard.

So basically it's like: 1BL -> 2BL -> patch kernel and HV and start them -> boot dashboard.

Every step also checks signature for the next step of course.

There are 3 kinds of verification used during boot:

- RSA signatures. CB and CF are RSA signed. No way to break this (MS has private key) basicly because it uses assymetric crypto. This prevents us from changing the boot code itself.
- SHA1 hash: CD, CE, CG. These hashes are contained in the RSA signed part of the previous sections and we can therefore not break it (also not time attackable). These can essentially be seen as extentions of the RSA signatures in CB and CF. Again preventing us from modyfing the boot code itself.
- SHA1-HMAC authentication. This is done in CB and CF too (but your CPU has the key). This prevents you to choose between released versions of the boot sections/dash etc. However this was time attackable.

Rumor says that the Xbox Live Servers are running a hash check on the HV (Hypervisor) which is stored in CE (5BL), and if the hash check returns false then it will deny you access to the server. So i am guessing that you would need to somehow return the hash checks as true. the same as it would on a retail 360's boot process. Correct me if i am wrong but that is what i am led to believe.

- Louis