The term “SHSH blob” is unofficial and based on abbreviations for (digital signature) and binary large object . Apple‘s official name for this process is System Software Authorization. The process is controlled by the TATSU ("TSS") Signing Server (gs.apple.com), where updates and restores can only be completed if the version of iOS is being signed.
Jailbreak exploits are often specific to certain iOS versions. If a new jailbreak is released for iOS , but you are on , you cannot update to because Apple is likely already signing . If you saved blobs for shsh blobs
Apple checks if that version is still "open." If it is, they send back an SHSH blob. The term “SHSH blob” is unofficial and based