How secure is Preupgrade?

[Björn Persson]

Preupgrade is clearly a good idea. There's just one thing with how it's 
implemented that I'm wondering about: What does it do to check the files it 
downloads for malicious tampering?

I can check the signatures on the RPM packages "manually" before I proceed 
with the upgrade, but as far as I can see there are no signatures on the 
files that it puts in /boot/upgrade. How are those checked? And what about 
files that Anaconda downloads during the actual upgrade? Does it check any 
signatures on those?

Björn Persson