Starting with iOS 5, Apple introduced a —a random number generated for each restore request. This means you can't just "replay" an old blob; the blob must match the specific nonce your device is currently expecting. Advanced tools (like FutureRestore ) are often required to manage nonces and successfully use your saved blobs for a downgrade. Engineering Security - School of Computer Science
Apple typically only "signs" the most recent version of iOS (and sometimes the one immediately preceding it). This is known as the . Once Apple stops signing an older version, it becomes impossible for a standard user to downgrade to it. SHSH Blobs are essential for: shsh blobs
Without this digital signature, your device will refuse to boot or install the operating system. Why Do They Matter? Starting with iOS 5, Apple introduced a —a