We stated in our downgrade guide that you can only downgrade to a firmware that Apple is actively signing. But for the jailbreak community, there is a loophole: SHSH Blobs.
What is an SHSH Blob?
Whenever you install an IPSW file, Apple's server generates a unique cryptographic signature for your specific device (tied to your ECID) and that specific iOS version. This signature is the "Blob".
By saving this signature while the firmware is still being signed by Apple, you can theoretically use specialized tools (like FutureRestore) to "replay" that signature later, tricking your device into installing an unsigned IPSW.
The Catch
In modern iOS versions (iOS 16+), Apple introduced Cryptex1 and tightened SEP (Secure Enclave Processor) compatibility, which has made downgrading with SHSH blobs incredibly difficult or outright impossible for most A12+ devices. However, saving them is still considered best practice in the jailbreak community.
Related Guides
If you are troubleshooting Apple firmware issues or managing device updates, explore our other step-by-step guides: