We are currently living in the iOS 5 era, and there's a lot of iPhone, iPod and iPad users upgrading to iOS 5 accidentally or sometimes on purpose just to test their devices with the so-called successful and improved operating system. If you however feel like downgrading at a certain point from any iOS version, you must read the following.
Before you proceed or attempt to proceed with a software downgrade, you must understand how an iDevice restoration works.
When you hit the "Restore" button using iTunes, whether you select a custom firmware or not, iTunes will connect to Apple's servers and attempt to get a digital signature so that they approve the device firmware to be installed.
If Apple determines the firmware is too old, not compatible, or invalid, it won't sign the restoration and iTunes will return an error code when attempting to restore your device.
Usually after Apple has released a new firmware, it may take several weeks for Apple to stop signing previous firmwares. However, it is normal if Apple decides not to sign previous firmwares versions just hours after releasing a new firmware, just like it happened after releasing iOS 5.
We call firmware to the operating system running in your iPhone, iPod or iPad, also known as iOS.
You may have heard about people being able to downgrade their devices at some point, and you might be wondering: How is possible to downgrade when Apple is no longer signing old firmware versions?
You may have found a couple tutorials through the web, and you have heard about blobs and SHSH and other non-familiarized terms, and you're maybe stuck at a point where you can't turn back. Maybe you are frustrated and you don't know how to proceed.
That's why we always suggest and we always advice:
DO NOT UPDATE YOUR DEVICE! IF ANY OF THE FOLLOWING:
1. If you don't know how to downgrade or know if it's possible to downgrade. (Thinking that it may be possible, is not being sure, so don't proceed unless you are 100% sure about that).
2. If you rely on Jailbreak or unlock. (Specially with iPhone 4, you won't be able to unlock your device if you upgrade, at least until a new unlock method is released which we may never see since developers are working on iPhone 4s, and leaving iPhone 4 in oblivion).
You may however be thinking about downgrade methods posted around the web. Be aware IT IS possible to downgrade to an old firmware which is no longer signed by Apple. However, the following criteria must be met in order to downgrade:
A) THE DEVICE WAS PREVIOUSLY JAILBROKEN USING AN OLD FIRMWARE. (If you accidentally upgraded to iOS 5.0, but your device was jailbroken while on iOS 4.1, you can downgrade to firmware 4.1).
B) YOUR BLOBS WERE PREVIOUSLY SAVED WHILE ON AN OLD FIRMWARE. (If you are not familiar with this term, or don't know how to do that, refer to this link http://www.saurik.com/id/12 so that you get familiar with it. If you upgraded already to the latest firmware, this will not work).
C) THE FIRMWARE IS STILL BEING SIGNED UP BY APPLE. (The best way to determine whether is signed or not, is to attempt to restore to that specific firmware).
D) YOUR HOSTS FILE HAS SAURIK'S SERVER CACHED. (Refer to the URL in step B).
The big question: HOW TO DOWNGRADE?
1. PLACE YOUR DEVICE IN DFU MODE. (DFU mode is not the same as restore mode).
To enter DFU mode:
a) Plug your device into the PC.
b) While turned on, press and hold both power and home button for 10 clock seconds.
c) Release the power button at the 11th second without releasing the home button and hold it until you see iTunes detecting your device in "recovery mode". Your device's screen should be completely black.
2. RESTORE USING iTUNES TO THE OLD OR CUSTOM FIRMWARE YOU WANT.
To select a specific firmware from iTunes:
a) Plug your device into the PC.
b) Press and hold shift if in Windows or Option if in Mac, and then click on "Restore" from iTunes.
c) Browse for the desired firmware, and iTunes will start the restoration. (THIS ONLY WORKS IF THE ABOVE CRITERIA IS MET).
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