Before downgrading your iPhone firmware from iOS 4.3 to 4.2.1, you must have SHSH Blobs for iOS 4.2.1. Why do you need to save SHSH blobs before downgrade iPhone firmware? It’s explained very well in this post: What is ECID SHSH Blobs The main point is, Apple will need to send signature approval back to … Continue reading How-to Downgrade iOS 4.3 to 4.2.1