Re: libgpod and ipod touch 4g database checksum hash

On Sat, 2011-01-01 at 17:23 +0100, Christophe Fergeau wrote:
> Hi,
> 
> 2011/1/1 jameskevindoyle <[email protected]>:
> > From other messages in the Ubuntu forums, it sounds like currently people
> > with the ipod touch 4g need to jailbreak it and downgrade the itunes
> > database version (I take it this makes it so the hash is one libgpod
> > supports?).
> >
> 
> I never heard of that, this used to work for iOS3, but Apple has fixed
> it since then as far as I know. If this is still possible, would be
> good to know.

I read about it in an Ubuntu Forums thread "New ipod touch 4g ios 4.1",
post #44 is the first place someone explains what to do
( http://ubuntuforums.org/showpost.php?p=10041131&postcount=44 ) and
someone else published detailed instructions after that at
http://cogizio.org/operating-systems/ubuntu/3089 .  So it sounds like
the database version change works for iOS4 (but with a jailbroken
device).

I'm not 100% sure I understand why changing the database version back
helps.  Does it mean that the ipod doesn't bother checking a checksum
when the older database version is in place?  Or does it mean it still
uses a checksum, but the checksum is computed differently from the newer
database version?  I'm only just learning a little about how ipods work
and trying to learn enough to understand how the different pieces of
Linux software work and why different software versions might be
required.

> 
> > I can't find any news anywhere, though, about whether there's active
> > development on implementing the new hash for libgpod (which would mean ipod
> > touch 4g owners wouldn't need to jailbreak?)
> 
> If you give us an explanation/specification about how this hash is to
> be computed, then it will get implemented. The blocking point is the
> former, not the implementation by itself.

I think I see.  How does the ipod touch 3g work compared to the 4g?
Does it also require computing a hash, but with a different hash
algorithm?  If so, who first came up with a specification for that hash
for the 3g?  It must have been reverse engineered rather than released
by Apple, right?

Thanks for your time.  It's very useful to understand why things work or
don't work, it gives me more credibility with my family.  :-)

Thanks,
Jim



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