Thanks to Saurik for all of his hard work. Below is his explanation from saurik.com on how to downgrade your iPhone 3G S for fiirmware 3.1 to firmware 3.0 and also how to continue using his server for future Apple firmware updates. Saurik did a great job at explaining how and why this downgrade works and I invite you to read his article for detailed information.

Saurik Also States:

Upcoming 3.1 Exploit

If you encouter “unknown error (3002)”, you probably do not have your ECID SHSH’s for 3.0 “on file” with Cydia. Unfortunately, as Apple is no longer allowing users to sign the 3.0 firmware, it is no longer possible to register your device with Cydia.

Luckily, it has been reported that iPhoneOS 3.1 is vulnerable to another exploit. This means that, once a jailbreak is released for 3.1, users be able to prepare themselves for future jailbreaks even if they missed the first round of signature storage (which I unfortunately was only able to start very late in the 3.0 game).

Once you even attempt to use this service (or if you tell Cydia to “make your life easier”) you will be signed up for the signature tracker, and Cydia HQ will do its best to manage your ability to restore.

And again, if you have any issues with this process, please please please do not e-mail me. Instead, go to ModMyi.com, where there is a special forum called 3GS Downgrading, created for the purposes of this article.

1. First, you must have saved your ECID file through Cydia. If this was done, you should see the following message at the top of Cydia’s homepage: This iPhone 3G[S] has an ECID SHSH on file.

2. Now we’re going to duplicate the functionality exposed by Apple’s signature server and trick iTunes into thinking it is connected to Apple’s servers. Make sure you have iTunes 9 installed on your computer:

On a Mac, go to /etc/hosts. On a PC, go to C:\Windows\System32\drivers\etc\hosts. Open the file in a text editor and add the following entry at the bottom of the file: 74.208.105.171 gs.apple.com

Save the file and close it.

3. Now we have to put your iPhone into DFU mode. To do this, open iTunes, plug your iPhone and hold down the power and home buttons for 10 seconds, then let go of the power button but continue to hold the home button 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.” Your iPhone screen should be completely black.

Note: 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. You may read my article on how to put your iPhone in DFU Mode.

4. You can now do a “normal” restore to the 3.0 software. To do this, hold down the Option key (on Mac OS X) or the SHIFT key (Windows) while clicking the Restore button in iTunes. Select the firmware 3.0. Download iPhone OS 3.0 here for iPhone 3GS.


TroubleShooting & Fixes

If you get the “unknown error (3002)”, it’s because you probably don’t have your ECID SHSH’s for 3.0 on file with Cydia and it is unfortunately impossible to register your device with Cydia anymore. There is no solution, your iPhone can’t be downgraded from 3.1 to 3.0 and you’re gonna have to wait for a new jailbreak.

If you get the “The iPhone “iPhone” could not be restored. An unknown error occured (1015)” error, then re-do the process all over again. You will get the same error again and it is normal. Ignore the error and jailbreak your iPhone using RedSn0w.

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