The easiest way to backup your signatures without downloading heavy software is through online community platforms.
When iTunes restores or updates an iOS firmware, Apple has added multiple checkpoints before the iOS version is installed. At the first "Verifying iPhone software" stage, iTunes communicates with "gs.apple.com" to verify that the IPSW (iOS firmware file) is still being signed. The TATSU server returns a list of versions currently being signed.
Saving blobs “doesn‘t guarantee a safe downgrade on modern iOS,” as even valid blobs may be insufficient if SEP or baseband incompatibilities arise. For devices from the iPhone XS (A12) and newer, SHSH blobs have effectively become obsolete due to nonce entanglement combined with the inability to set custom nonces on stock firmware. shsh blobs
Blobsaver is a cross-platform GUI and CLI application for automatically saving SHSH blobs. It supports macOS, Windows, and Linux, and offers these features:
Once a firmware version is "unsigned," Apple's servers will refuse to generate the SHSH blobs for it. Without that real-time digital signature, iTunes or Finder will throw an error (such as the infamous Error 3194), and the installation will abort. Apple enforces this restriction for two primary reasons: The easiest way to backup your signatures without
If you are currently attempting to change your firmware version, let me know: What are you using?
Since iOS 5, Apple introduced a nonce —a per-request random value—to prevent attackers from simply reusing old, saved signatures. The TATSU server returns a list of versions
BlobSaver is a popular, cross-platform tool (Windows, Mac, and Linux) that simplifies the process.
Apple enforces strict control over the iOS ecosystem through a mechanism known as the "signing window." When a new iOS version is released, Apple typically stops signing the older version within a few days or weeks.