As with most consoles, there is a dev kit that is sold to legimate game developers that includes the required libraries to make the game, specs, usually a console that is hooked up to a computer so that games can be send to the console or sent to a hard drive on the console or streamed from a pc, etc, etc. They will usually boot unsigned or unprotected code on the console. Obviously, the game is only signed at the very end stage. The key is having a dev kit but they are usually only sold to legimate developers and cost lots and lots of money. With the original XBox, the development software was leaked to the public from a game developer, hence why we even have homebrew software. Until those libraries are leaked from the 360, even if we get a chip that could boot unsigned code, no one has any tools to make any 360 software anyways. From what I've read, the 360 SDK is heavily watermarked with each developers key/code or something, making it a huge risk to whoever would leak it.