Tech Info

Bypassing the Overlord

To this end, I have constructed a server that duplicates the functionality exposed by Apple's signature server, except using "on file" results rather than live requests.
All we need, then, is to make iTunes use it. Luckily, most operating systems also have the ability to locally define bypasses on specific hostnames through a file called hosts. Using this, we can redirect requests to Apple's signature server to Cydia.

So, open the file C:\Windows\System32\drivers\etc\hosts (Windows) or /etc/hosts (Mac OS X) and add the following entry to the bottom of the file.

74.208.10.249 gs.apple.com

Now, when iTunes thinks it is talking to Apple, it is talking to Cydia instead. Doing this will allow iTunes to access signatures already stored by Cydia's "on file" feature.

This server will also act as a cache for any SHSH blobs it hasn't seen, acting as an intermediary to Apple's server. This effectively registers your device with the "on file" mechanism, which means you can now enjoy the protections of being able to downgrade your firmware in the future even if you aren't jailbroken.

This point should be stressed: even if you don't jailbreak, and even if you never intend to jailbreak, you should consider using the new "on file" service.
Let's say that Apple releases an OS upgrade in the future, you take it, and they break something important. Maybe they break your e-mail account, or your todo list. Your business is now crippled.
If only you could downgrade, right? Alas, Apple won't let you anymore. That's where the new signature cache server comes in: by doing your restores through this server you secure your ability to not accept upgrades from Apple if the need is dire.

Performing the Restore
Now, one would have hoped that the process would be as easy as "restore using the 3.0 IPSW". If only we were that lucky. The first problem is that a downgrade from 3.1 to 3.0 must be initiated in DFU mode.
So, we begin: hold down the lock and menu buttons (some call these the power and home buttons) for 10 seconds, letting go of the lock button but continuing to hold menu until iTunes recognizes the device with the message: "iTunes has detected an iPhone in recovery mode. You must restore this iPhone before it can be used with iTunes.".

Note that, at this point, your iPhone's screen should be entirely black. Many people confuse "DFU" with "recovery" (and in fact, iTunes itself glosses over this), but they are quite different. If you see anything on your screen, such as the iTunes logo and a sync cable, or a cartoon of Steve Jobs swearing in Cyrillic, you are in recovery mode and need to try again. One can find videos online that may help.

At this point, you should do a "normal" restore to the 3.0 software. When doing this, remember to hold down the option key (on Mac OS X) or the shift key (Windows) while clicking the Restore button in iTunes. Select the firmware (which is probably named iPhone2,1_3.0_7A341_Restore.ipsw), and things should be on their way.
Please note that I do not have signatures for 3.0.1, only for 3.0. For some very small number of users I also have a signature for 3.0.1, but I ran out of time hitting the Wednesday deadline getting the code for this working and generalized. If you would like to try restoring to 3.0.1 with my server, therefore, to see if you have 3.0.1 keys on file you can try, but it may fail late in the process with a very weird error. All users "on file", however, have 3.0 ready to go.


Thanks
DJRaz55