Is it Possible to Downgrade from iOS 7.1.1?
Whenever Apple pushes out some latest software update, we as users update our iPhone and iPad as quickly as possible for us. While many of these incremental updates bring some good fixes, often things go rather worse. It is at those times when we try to downgrade to earlier versions of the OS. Here we will see if it’s possible to downgrade iOS 7.1.1, which is the latest in the series of updates.
Downgrade iOS 7.1.1:
In order to keep the latest updates from getting jailbroken, Apple has stopped signing the firmware files. This thwarts the chances of us to downgrade iOS 7.1.1 or iOS 7.1. It also means that we can’t update an older version of OS too.
Reported by iPhonehacks, here is the detailed explanation by iPhone Dev team on how Apple made it difficult to downgrade iOS 7.1.1 to any older OS version:
“Starting with the iOS5 beta, the role of the “APTicket” is changing — it’s being used much like the “BBTicket” has always been used. The LLB and iBoot stages of the boot sequence are being refined to depend on the authenticity of the APTicket, which is uniquely generated at each and every restore (in other words, it doesn’t depend merely on your ECID and firmware version…it changes every time you restore, based partly on a random number). This APTicket authentication will happen at every boot, not just at restore time. Because only Apple has the crypto keys to properly sign the per-restore APTicket, replayed APTickets are useless.
This will only affect restores starting at iOS5 and onward, and Apple will be able to flip that switch off and on at will (by opening or closing the APTicket signing window for that firmware, like they do for the BBTicket).”
– Source and more details: iPhoneHacks