How can I downgrade my iPhone firmware from iOS 4.3.4 to 4.3.3?
So for whatever reason you went ahead and updated your iPhone to iOS 4.3.4 in iTunes. Normally this is no problem, except for the fact that your want to jailbreak your device untethered. Turns out an untethered iOS 4.3.4 jailbreak solution doesn't exist right now. Is there any way to return to iOS 4.3.3 and jailbreak?
Downgrading is relatively straightforward if you have already saved your SHSH blobs. Follow these steps to downgrade to earlier firmware, including iOS 4.3.3, 4.3.2, 4.3.1, 4.3, or 4.2.1.
1. Locate and download the firmware file (IPSW) for the iOS version you are downgrading to. Save this file on your computer. Find the file you need here:iPhone 4 IPSW files
Verizon iPhone 4 IPSW files
iPhone 3GS IPSW files
2. Connect your iPhone to your computer via USB and start iTunes.
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3. Put your iPhone into Device Firmware Update (DFU) mode. You can read how to put your iPhone 4 into DFU mode here, or read how to put your iPhone 3GS into DFU mode. A message like the one below should appear and the iPhone screen will remain black.
4. You must edit the hosts file on your computer to use your saved SHSH blobs. To do this on Mac OS X click the Go -> Go to Folder menu in the Finder.
Go to the folder /etc and copy the file 'hosts' to your desktop. Edit the file with TextEdit and add this line to the end of the file:
Save the modified hosts file, then drag it into the /etc folder and overwrite the old file.
Windows users will find the hosts file in C:\Windows\System32\drivers\etc\ and can open the file using Notepad. In order to edit the hosts file, Notepad must be run with Administrator Privileges. Right-click the Notepad icon and select Administrator Privileges to run in this mode. Add this line to the end of the file and save:
5. Return to iTunes and select your iPhone from the left menu under DEVICES. On the Mac, hold down the option key (alt) and click the Restore button in iTunes. Using Windows hold down the shift key and click the Restore button in iTunes.
6. Find and select the IPSW file you downloaded in step one. Click Open and iTunes will begin to restore your iPhone to the desired firmware. You will see a progress bar on the iPhone.
When the process is complete, your iPhone will reboot automatically and be running iOS 4.3.3 or whatever firmware you have opted to install. Don't forget to reedit the hosts file to remove the line '126.96.36.199 gs.apple.com' after you finish downgrading. This way iTunes will use Apple's servers for future updates.