The Fedora Project recently re-signed all of its packages with a new key. The story regarding the key can be found here. Contact the release engineering team via IRC in #fedora-devel (irc.freenode.org) or via email to firstname.lastname@example.org for more information.
The final stages of testing are being done on new builds of the fedora-release, PackageKit, gnome-packagekit and unique (new dependency for gnome-packagekit) packages. This means that updates will soon be pushed to their appropriate locations and available for download. Once these initial packages have been installed the next update attempt will point to the new repositories utilizing the new signing key. Users need to accept the new signing key the first time updates are downloaded. PackageKit prompts you whether or not to import the signing key. To accept the key, press y at the prompt.