Specifically for those wanting to jailbreak the iPad, the subject of SHSH blobs is one that you should get to understand.
SHSH Blobs Defined
An SHSH blob (short for Signature HaSH, blob simply referring to a blob of data) is basically a digital signature that the Apple Server uses to approve a restore process for iOS devices such as the iPad.
Why Do You Need to Save SHSH Blobs?
In order to understand why it is important to save SHSH blobs if you want to jailbreak, we are going to explain it in the context of the role it plays during a restore process.
During a restore process you open up iTunes on the computer, connect your iPad via the supplied USB cable and once the device is detected, you proceed to click on 'Restore'. What happens then is that iTunes will send a restore request to the Apple server. The Apple server will have to respond by either rejecting or approving the request which will depend on whether the firmware that you are requesting to restore to is the current version available; 'current' here meaning whatever firmware versions Apple is still approving.
If the Apple server approves the request, it will send a digital signature back to iTunes which is called an SHSH blob. Only then can the restore process happen.
An 'EXAMPLE' Scenario: Let's say that the latest jailbreak only works for iOS 4.3.3 and Apple has already released 4.3.4. They have also stopped signing/approving restore requests for 4.3.3. One fine day after installing some jailbreak apps on Cydia, your iPad suddenly has an error which requires you to restore the device (not common, but it can happen). Now if you have saved your SHSH blob for 4.3.3, you can use it to trick iTunes (more on how to do this in a different iML tutorial) into thinking the Apple server has signed/approved the restore request and thus be able to restore to a firmware that can be jailbroken; in this case 4.3.3. On the other hand, if you did not save your SHSH blob, you will be forced to restore to 4.3.4 which you will not be able to jailbreak. And if you are wondering why you can't just get the SHSH blob from a website or someone else, it is because the SHSH is attached to your iPad's ECID which makes each blob unique
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