iTunes packages up this valuable information and sends it to your device. Apple takes the firmware version files and combines them with your ECID and generates a hash that ONLY APPLE can generate. It is signed with a unique id ( ECID) that only your device has. See, the firmware is now signed for the below devices. The way they stop you is basically by a simple response that iTunes receives when you try to restore the firmware of your choosing. Once you ‘upgrade’ they don’t let you downgrade. When you try to restore an older firmware on the devices listed below, Apple won’t let you do that. For those who don’t know what the Firmware Umbrella and TinyTSS are, check the details below along with the Download Links… TinyUmbrella is a unified version of FirmwareUmbrella and TinyTSS. Notcom has released TinyUmbrella to save SHSH blobs for iPhone, iPad and iPod Touch.
