Apple checks if that version is still "open." If it is, they send back an SHSH blob.
Popular community tools like TSS Saver (online) or Blobsaver (desktop application) can automatically fetch and store these for you. shsh blobs
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: Apple checks if that version is still "open
Without this digital signature, your device will refuse to boot or install the operating system. Why Do They Matter? This is known as the
Many jailbreaks are only compatible with specific, often older, versions of iOS. Saving blobs allows you to "hop" to those versions later, even after Apple has closed the signing window. How the Process Works