IDEA: A private encrypted entry area, sort of "private description" for the "owner" of the giveaway

and why not keeping it anywhere else on the internet (for example on pastebin, having spreadsheet on dropbox etc).

SG is about managing GAs and community - your idea have nothing to do with neither gifting not community - hence is not needed at all.

Keeping CD key in the system is never a good idea to begin with
Admins simply wouldn't take the risk of storing keys in the server

Why would it be a hassle to keep them as a text file in your desktop?

The key for the giveaway isn't related to the giveaway?