Apple has stopped signing iOS 10.1.1 firmware version for all the iOS devices like iPhone, iPad and iPod Touch which means that users can no longer downgrade their iOS to that version using iTunes officially.
Now you can’t downgrade to iOS 10.1.1 on iPhone, iPad and iPod touch, as Apple stops signing iOS 10.1.1 firmware version so if you are on lower iOS version you can downgrade and upgrade to iOS iOS 10.1.1. So basically you are forced to upgrade to iOS 10.2 directly. If you have accidentally update your device via OTA, then there is not way to downgrade back to iOS 10.1.1 now as Apple stops signing iOS 10.1.1.
Apple always gives two versions of iOS to restore whenever it releases a new version. So that people have ability to downgrade their devices to the previous version if they are not satisfied with the new one. But after some time, it stops signing the previous version.
You can also visit this link https://ipsw.me to check the signing status of Apple firmware.
Note: If you are on lower iOS versions like 10.1, 10.1.1 stay away from update because jailbreak is only available on lower version of iOS. If you are a jailbreakers, do not upgrade to iOS 10.2 as there is no jailbreak for iOS 10.2. So it’s better to stay on older version of iOS for now.
Another good news for jailbreakers, iOS hacker tihmstar has announced the upcoming release of his tool Prometheus that allows you to downgrade and upgrade unsigned iOS 10.1.1 on iPhone, iPad and iPod touch by which you will always be able to jailbreak your device at any time even after Apple stops signing the iOS 10.1.1. Prometheus tool works on 32-bit and 64 bit enabled iOS devices as said by Tihmstar.
For this you need to save .shsh2 blobs. To save .shsh2 blobs for downgrading and upgrading an unsigned iOS firmware like iOS 10.1, iOS 10.1.1, you first need to go to tihmstar’s GitHub and download tsschecker tool which supports Mac, Windows and Linux.
