I usually get packages from http://f-droid.org/ repository through their package browser (because then I have a guarantee that I use free (= libre) software); and they are signed with their key.
I use CyanogenMod 10; and I have root access.
I don't like allowing packages from "unknown sources" for this.
Can I set up the system so that f-droid counts as a known source, and packages from all other unknown sources are not allowed to be installed by default as before.
Perhaps, something can be patches in the CyanogenMod distro to add f-droid's key as a key for a "known source" of packages.