This tutorial will teach you how to back up your SHSH blobs using TinyUmbrella
Currently Apple is only signing 4.0.2 signatures, so only 4.0.2 SHSH blobs will be saved!
This does work with non-jailbroken devices as well and it is recommended you save these SHSH blobs if you are considering to jailbreak/unlock in the future.
This guide only applies to the following devices: iPhone 3G[S], iPhone 4, iPod Touch 3G, and the iPad
Step 1: Download the latest TinyUmbrella from here: http://thefirmwareumbrella.blogspot.com/
Step 2: Plug in your iDevice, Run TinyUmbrella, and hit advanced:
Step 3: Hit Save My SHSH
Step 4: Check the status of the SHSH backup
Step 5: Check if the SHSH blob has successfully backed up
Congratulations! You have successfully saved your 4.0.2 SHSH blob!