(Last Updated On: June 12, 2020)
SHSH Blob is short for Signature HaSH file which is verified against Apple Firmware Verification Server to verify the the iPhone is running the latest version of iOS. If for some reason, when you are try to restore to a previous version, Apple will not allow you to restore it. This is because Apple is preventing you from using older version of the software that can be jailbroken and unlocked.
To make this possible, we need to send a request to a different server (Local or designated) which sends a SHSH blob (which was saved by you) back to iTunes faking that it is the current version.
If you have an iPhone 3G, 3GS, 4, iPod Touch 2G, 3G and iPad you need to save your SHSH blob.
How do you save your SHSH blob?
Method #1: Launch Cydia and Tap on “Make my life easier, thanks!” once you done this, after few minutes it should say “This device has SHSH on file for iPhone OS XXXX“.
Method #2: Using Firmware Umbrella – details to follow.
Method #3: Download AUTOSHSH. Connect your iPhone 3GS / iPod Touch 3G and run AUTOSHSH. That’s it.