Shsh Blobs Page

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.

To understand SHSH blobs, one must first understand Apple’s verification process. Every time an iPhone, iPad, or iPod touch is restored or updated, the device sends a request to Apple’s signing server for a permit to install the firmware. The server responds with a unique SHSH blob—a digital signature tied to that specific device (via its ECID, or Exclusive Chip ID) and that specific firmware version. Without a valid blob, the restore fails. This process ensures that users cannot install older, potentially vulnerable firmware versions that could be exploited for jailbreaks or security research. Once Apple stops “signing” a particular iOS version, the server will no longer generate valid blobs for it. shsh blobs

However, the Tiva Signing mechanism has made it more challenging for users to jailbreak or downgrade their devices, as it's more difficult to obtain and verify SHSH blobs. You save the signature to your hard drive