If you have upgraded to the iOS4 firmware and are not happy with all the incompatible apps or just want to revert back to the 3xx firmware generation, then there may be light at the end of the tunnel. As you know every time you upgrade your firmware version it means Apple stops signing the previous firmware version; meaning technically you cannot downgrade your iPod Touch or iPhone. However, if you were smart and managed to save your ECID SHSH File on Saurik’s servers, then you may be able to downgrade your iPhone from iOS 4 to 3.1.3 or earlier.
When you save this ECID SHSH file through Saurik’s servers it tricks iTunes into believing that it is requesting a signature from Apple’s servers, while it will actually requesting the signature from Saurik’s servers.
The bottom line is, is that if you have saved your ECID SHSH file through Cydia then you CAN downgrade to the 3.1.3 firmware or even earlier. If you did not save your ECID SHSH file and you have upgrade to the iOS4 firmware generation then you CANNOT downgrade to the 3.1.3 firmware.
Learning How To Downgrade iOS4 To 3.1.3
**Note – For the first step of this tutorial there will be two different paths to follow depending on your operating system. If you are running Windows then follow the Windows labeled Step One and for Mac users follow the Mac labeled Step One.
For Windows Users (Step 1)
The first thing you are going to need to do is pre-check to make sure you are logged in with administrator privileges. When you have these administrator privileges then you will need to navigate to the following directory.
Once you have navigated to the directory above you will need to open the hosts file. This file is named exactly as shown and has no file-type extension (It is important to remember this when saving your hosts file). Open this hosts file in a text editor of your choice (EX: notepad) and then dd the following at the very bottom of the file: 126.96.36.199 gs.apple.com
Once you have added the line shown, save the file back where you found it (with no file type-extension). Once you have done all of this you can continue to Step 2!
For Mac Users (Step 1)
If you are running mac the first thing you are going to need to do is launch Finder. Once finder is up and running select Go To Folder, and enter /etc into the file pane. Once you are in the /etc directory you will need to search for the hosts file (This file has not file-extension and it is important to remember this when saving the file). Once you have found the hosts file, right click on it to open with TextEdit. When the file is open in TextEdit you will need to add the following at the very bottom of the file: 188.8.131.52 gs.apple.com
Once you have added the line above into the hosts file Click Save As and save the hosts file to your desktop keeping its original name enacted (hosts). Make sure that you un-check the box that says “if no extension is provide, use .txt”. Once the file has been saved to your desktop, drag and drop this edited file to the /etc directory.
Step 2:) - Once you have completed either Step 1 for MAC or Step 1 for Windows you will need to download the firmware you want to downgrade to from here. Once the firmware file of your choice has downloaded continue to Step 3.
Step 3) - The next thing you will need to do is plug your iPod Touch or iPhone into your computer. Once it is connected and iTunes opens stop iTunes from Syncing and Exit iTunes completely. Once iTunes has exited then you will need to put you iPod Touch or iPhone into DFU mode; you can find detailed instructions by clicking here. In short you need to Press and hold the home and and sleep button together for 10 seconds. After exactly 10 seconds, release the sleep button while still holding the home button. Keep holding the home button until iTunes re-opens asking you to restore your iPod Touch or iPhone.
Step 4) - The last thing you need to do now is actually restore your iPod Touch or iPhone. Do this now by holding the Option key (Mac only) or the Shift key (Windows only), while clicking the Restore button via iTunes. Once you click this restore button holding to according button, a dialog box will pop up and you’ll be able to choose the firmware you downloaded in step 2.
Your iPod Touch or iPhone should now restore normally to the firmware file that you chose in step 2. If you find that your iDevice is stuck in recovery mode then you will need a tool to fix this fairly common restore error. To fix this error you can simply download and launch iReb for Windows or iRecovery (both Mac and Windows). Congratulations if you have successfully downgraded your iPod Touch or iPhone from the iOS4 firmware to the 3.1.3 firmware or earlier. If you did not get success or you need some help you can go to the Graveyard and I will help you accordingly. You can also leave any questions/comments in the comments section below!