Downgrade iPhone 3GS OS 4 beta to 3.1.3 with Cydia SHSH

Apple released OS 4.0 Beta one for iPhone developers to develop and test their applications with new API released with iPhone SDK 4.0. As usual beta firmware leaked within a hour on torrent, rapidshare and other popular file sharing sites. In order to install iPhone OS 4.0 Beta on your iPhone/iPod Touch, you need to register your unique device id (UDID) via Apple developer subscription. Lots of registered developer are adding UDID for $6 to $15 per iPhone. Back to downgrading, If you guys updated your phone to OS 4.0 and wanna get back on OS 3.1.3 or below, following is the step by step guide to downgrade your iPhone 3GS OS 4.0 to 3.1.3 or below.

But you can Download the iPhone OS 4 beta [Direct Links] From Here

The process is very simple all you have to do, is to add Sauriks Server address to your system hosts file. This trick make iTunes thinks it is talking to Apple, it is talking to Cydia instead while the restoring process. Doing this will allow iTunes to access signatures already stored by Cydia “on file” feature. In simple words this duplicates the functionality exposed byApple’s signature server, except using “on file” results rather than live request.

Note:

This process is only for those who saved their SHSH to Cydia Server already.
Don’t use this procedure for 3.0.1, because Saurik Server do not have signatures for 3.0.1
Read the entire post two-three times before starting the process.
iPhone unlockers note that by doing this you can downgrade your firmware only, your baseband is still at 05.13.03 which is un-hacked at the moment.

How to Edit and Save Hosts file in Windows:

Open Notepad with Administrative privileges by clicking Start, All Programs,Accessories, and then right-click Notepad and select to open as Administrator.

74.208.10.249 gs.apple.com

Now you navigate to files menu and save the hosts file. By doing this you changed the communication server, and then we will ensure that iTunes checks the firmware on the server rather than opens Saurik to Apple! Because your ECID is on that server, the verification will fail and restore the previous version will be done without too many problems.

How to Edit and Save Hosts file in Mac OS X:

Navigate to /etc and look for hosts file, right click on hosts file and open with Text Edit, and add the following entry to the bottom of the file.

74.208.10.249 gs.apple.com

Now save the file and click on Save As.
Because Text Editor can’t save your system files, here comes the tricky part, in save as windows use the following settings:

In Where locate to Desktop
Uncheck the “ If no extension is provide, use .txt “ and then press the save button.

A host file will be appear on your Desktop, just drag and drop to /etc and follow the onscreen instructions.
Press the Replace and enter your Password

By doing this you changed the communication server, and then we will ensure that iTunes checks the firmware on the server rather than opens Saurik to Apple! Because your ECID is on that server, the verification will fail and restore the previous version will be done without too many problems!
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Now you can do your Normal Restore to 3.1.3 (with Recovery Mode) and Downgrading from 4.0 to 3.1.2 or below (with DFU Mode). For more details on Recovery Mode and DFU Mode

To Downgrade iPhone 3GS from 4.0 to 3.1.2 or below :

Cross Check : You must have edited the host files to Sauriks server as guided above and you must have SHSH saved on Cydia. If yes you may proceed further.
Step 1: Put your iPhone in DFU mode with following instructions.

Connect your iPhone to your computer.
Turn iPhone off.
Hold power and home together for 10 seconds (exactly).
Release power but keep holding home until the computers beeps (observed on a PC) as a USB device is recognized.
A few seconds later iTunes should detect your iPhone.
If the Restore Logo is present on the screen, you are in Recovery Mode, not DFU.

Step 2: Once your iPhone is in DFU mode following message will be appeared in iTunes. Click on “OK” , Now hold Option key while clicking Restore in iTunes and browse the OS 3.0 firmware for your iPhone 3GS. Now the restore process will take 10 – 15 minutes.

If you encountered an error message like 1011, 1013, 1015, just ignore them(Actually the firmware 3.0 is already successfully installed). Simply launch RedSn0w and do the Jailbreaking Unlocking process again. Check our guides on Jailbreaking iPhone here.

But if you encountered with error message like 1601, 1602, 1600 or anything else then try putting the iPhone into DFU mode and try again.