The creator of sn0wbreeze – iH8sn0w – has done it again, he provided the jailbreak community a new type of jailbreak tool – called iFaith – that allows users to downgrade their installed iOS version to an older one – but only if they have backed up their SHSH blobs.
Backing up your SHSH blobs is an important step. Without them, you won’t be able to downgrade your firmware in the future when Apple releases updated firmware and stops signing the old.
Unlike the TinyUmbrella utility developed by @notcom, iFaith features the ability to create custom firmwares that are stitched together with your saved SHSH blobs. It’s good to mention that iFaith has its own caching server – while TinyUmbrella relies on Cydia’s server for retrieving saved SHSH blobs.
Like redsn0w, iFaith has the ability to boot your iDevice in Pwned DFU Mode, which is a special type of recovery mode that’s necessary for iTunes to recognize and restore to custom created firmwares.
A special feature of iFaith is the ability to allow users to dump SHSH files for the old firmware running on the device even if Apple is not signing the firmware. So if you have an iPhone 3GS running iOS 4.2.1, you can dump the SHSH blobs with iFaith and later you can restore iOS 4.2.1 to your iPhone – even if Apple isn’t signing 4.2.1 anymore.