Shsh Blobs -

You save the signature to your hard drive. Later, when Apple stops signing the old version, you can trick your phone into thinking Apple said "Yes" by feeding it the saved blob.

: When you restore an iPhone, it requests a signature from Apple's servers. If Apple has stopped "signing" that version (usually about a week after a new release), the restore fails. shsh blobs

While SHSH blobs themselves are harmless data files, the downgrading process involves security risks: You save the signature to your hard drive

If the latest signed SEP firmware is structurally incompatible with the older iOS version you want to downgrade to, the restore will fail or break core security hardware features. As a result, even with perfectly saved SHSH blobs, modern downgrades are largely limited to versions that share SEP compatibility with currently signed firmware. If Apple has stopped "signing" that version (usually

An (Signature HaSH) is a unique digital signature that Apple uses to verify the firmware version you are trying to install on your device. Every time you restore or update your iPhone via iTunes or Finder, the software sends a request to Apple’s servers. Apple then "signs" this request with a blob specific to your device's unique ID (ECID) and the specific iOS version.

You can only save SHSH blobs for an iOS version . You cannot save blobs for an older iOS version that is already unsigned, even if that version is currently running on your device.

If a new update makes your phone slow or you dislike the features, you can only go back to an older version if you have saved the blobs for that specific version while it was still being signed.