Apple has finally rolled out the highly-anticipated iOS 11 public release on supported iOS devices with tons of new features and enhancements.
Like any new iOS release, the latest iteration may also harbor untested bugs or unoptimized features that could result in poor battery life and other performance issues.
Consequently, iOS 11 users may be forced to restore the previous iteration or downgrade back to iOS 10.3.3 as it is still being signed by Apple.
Key Points to Remember
Apart from iOS 10.3.3, you will not be able to downgrade iOS 11 to any other older firmware as they are no longer being signed by Apple.
This procedure involves wiping all the data on your device and then restoring the same from a backup. The amount of time consumed by this process depends on the size of the data backup as well as the speed of your internet connection (if using iCloud backup).
Ideally, you should avoid restoring iOS 11 data backup files on iOS 10.3.3 device (after the downgrade), as this could result in stability issues and corrupt system files. In other words, it is safe to restore from archived backup of iOS 10.3.3 data files on the same firmware version.
You can always verify Apple's firmware signing status for iOS by navigating to this website. If you see a green checkmark in the status field then that firmware is currently being signed by Apple and you can safely downgrade iOS 11 to the previous release.
iOS 10.3.3 IPSW Direct Download Links
iPhone
iOS 10.3.3 (iPhone 5 GSM): iPhone_4.0_32bit_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPhone 5 GSM+CDMA): iPhone_4.0_32bit_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPhone 5s GSM): iPhone_4.0_64bit_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPhone 5s GSM+CDMA): iPhone_4.0_64bit_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPhone 5c GSM): iPhone_4.0_32bit_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPhone 5c GSM+CDMA): iPhone_4.0_32bit_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPhone 6+): iPhone_5.5_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPhone 6): iPhone_4.7_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPhone 6s): iPhone_4.7_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPhone 6s Plus): iPhone_5.5_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPhone SE): iPhone_4.0_64bit_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPhone 7 GSM+CDMA): iPhone_7_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPhone 7+ GSM+CDMA): iPhone_7Plus_10.3.3_14G60_Restore.ipsw
iPad
iOS 10.3.3 (iPad 4 Wi-Fi): iPad_32bit_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad 4 GSM): iPad_32bit_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad 4 GSM_CDMA): iPad_32bit_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad Air Wi-Fi): iPad_64bit_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad Air Cellular): iPad_64bit_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad Mini 2 Wi-Fi): iPad_64bit_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad Mini 2 Cellular): iPad_64bit_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad Air China): iPad_64bit_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad Mini 2 China): iPad_64bit_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad Mini 3 Wi-Fi): iPad_64bit_TouchID_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad Mini 3 Cellular): iPad_64bit_TouchID_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad Mini 3 China): iPad_64bit_TouchID_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad Air 2 Wi-Fi): iPad_64bit_TouchID_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad Air 2 Cellular): iPad_64bit_TouchID_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad Mini 4 Wi-Fi): iPad_64bit_TouchID_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad Mini 4 Cellular): iPad_64bit_TouchID_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad Pro Wi-Fi): iPadPro_12.9_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad Pro Cellular): iPadPro_12.9_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad Pro 9.7 Wi-Fi): iPadPro_9.7_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad Pro 9.7 Cellular): iPadPro_9.7_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad 5 Wi-Fi): iPad_6,11_iPad_6,12_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad 5 Cellular): iPad_6,11_iPad_6,12_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad Pro 12.9 Wi-Fi 2nd Gen): iPad_7,1_iPad_7,2_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad Pro 12.9 Cellular 2nd Gen): iPad_7,1_iPad_7,2_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad Pro 10.5 Wi-Fi): iPad_7,3_iPad_7,4_10.3.3_14G60_Restore.ipsw
iOS 10.3.3 (iPad Pro 10.5 Cellular): iPad_7,3_iPad_7,4_10.3.3_14G60_Restore.ipsw
iPod Touch
iOS 10.3.3 (iPod touch 6G): iPodtouch_10.3.3_14G60_Restore.ipsw
Steps to Downgrade iOS 11 to iOS 10.3.3
Step 1: Download iOS 10.3.3 firmware for your device from the links given above.
Step 2: Launch iTunes from the dock on your iOS device
Step 3: Boot your device into DFU mode as follows:
• Press and hold the Home button and the Sleep/Wake button at the same time.
• Wait for 10 seconds, before you release the Sleep/Wake button. But, continue holding the Home button until your device gets detected via recovery mode in iTunes. Then click on the OK button.
Step 4: Press and hold the Alt/Option key (Shift in Windows) and then hit the Restore iPhone/iPad button.
Step 5: Choose the firmware file you downloaded earlier from the pop-up window and click the Open button. Click Restore and update button once again to confirm or continue with the restoration process.
Step 6: Click the Next button, followed by the Agree button and let iTunes go through the restore/downgrade process. The entire process would last for 10 to 15 minutes.
Step 7: Once the restoration completes, your iOS device will be running the latest signed version of iOS 10 or iOS 10.3.3 and you should see the white Hello screen. Follow the onscreen instructions to setup the device for first use, and then restore all your important data from the backup that you saved earlier.
[Source: iPhone Hacks]
