Your problem is that you have redirected your hosts file to Cydia by using TU incorrectly. You should have followed my guides on this site which are designed to avoid the problem.
Open TU. Switch to the Advanced panel, then UNTICK "Set Hosts to Cydia on exit", then close TU.
A restore of 4.3.5 will now succeed because you are correctly pointing iTunes back to Apples signing servers.