Sund0wn

Sund0wn is a downgrade utility for Windows written by iSuns9 that allows tether and untether downgrades for all models of the iPhone 3GS, iPhone 4, and iPod touch 4G. This is useful if you want to downgrade to an older iOS version from iOS 7, of which iFaith has not been updated to support yet. Even if you do not have valid SHSH, Sund0wn will still give you the option to downgrade to an older firmware (though it will require a tethered boot via redsn0w afterwards).

Credits

 * iSuns9 - author
 * geohot - limera1n Exploit