Hi everyone. Yes, yet another new user joins the PSPU forums and puts in their worth. Hopefully I won't inspire the mass flaming that seems to happen so often on these forums in the little time I've been reading them.
Firstly regarding downgraders, exploits and any other hack for the PSP that people can think of. My understanding from reading the posts here is that downgrading basically works by overwriting a file in the flash memory of the PSP so that it thinks the version number of the current firmware is v1.0, meaning you 'downgrade' the unit by 'upgrading' to v1.5. This was possible because of an exploit found in the TIFF library on the PSP which allowed abritary code to be run in an environment where the flash was accessible (VMH mode).
v2.01 of the firmware (which sadly came preinstalled on my own PSP) didn't upgrade much with the exception of patching this particular hole. However, no extra security measures were added. This means that if another exploit (such as the libungif holes that are being discussed right now) were to be found that had access to the flash (which means the GTA exploit is no good), the same method could be applied to downgrade a v2.01 PSP by first going backwards to v1.0 (or perhaps v1.01 if only the major version number is changed), then going back to v1.5 again.
v2.5 onwards have more security, which means that even if an exploit like libungif were to be utilised, a downgrader for this version of the firmware would be much more difficult to implement, if it were possible at all. v2.6 adds yet more security, and more than likely patches the holes in libungif making any work done with that exploit useless on that firmware.
The current GTA exploit that Fanjita is working on based on Edison Carter's work has no direct access to the flash memory. That means that there will never be a downgrader developed through this exploit, only EBOOT loaders and other software. However, these will require a person to have GTA to use them, and you will need to run GTA every time you want to run a particular piece of homebrew.
Do I have this right so far? Basically v2.0 can be downgraded due to the exploit having access to the flash memory, which was patched for v2.01 and above, which is why none of these supposed v2.01+ downgraders work properly. For a downgrader to be made for the newer firmware, another exploit needs to be found that provides access to flash. The _reason_ everyone tries to downgrade in the first place is because Sony didn't have any requirements for software to be digitally signed, meaning you can just run anything without having to worry about all these exploit loopholes.
Now assuming I have all this correct, I've got one more question. How do people know just what libraries are being used on the PSP? I'm not sure about Edison's GTA exploit, but both the TIFF exploit and currently the libungif exploit have been found because of people being aware of the software versions being used on the PSP. Is it just assumed that Sony are using these libraries? Or is there some way of finding out?
Thanks for the time everyone, and keep up the good work in defeating Sony's work at hindering development on OUR consoles.