SHSH Blobs: What are they?

Apple has always been on guard as to how they can prevent jailbreaking and for users to install tweaks that they do not approve. If before, we can always select the firmware we want to restore to, it's a different case now. Say you're on firmware version 4.0, you cannot select 4.1 to upgrade. Instead, you have to jump to 4.2.1 directly as this is the latest version as of this writing. To be able to downgrade, you have to save your shsh blobs by using a program called TinyUmbrella. You can download it here. 

By using the TSS Server on TinyUmbrella, you can skip the verification process set by Apple and you will be able to downgrade to any firmware version of your choice provided you have saved the blobs for that specific version.