Visit the home pages of the package repositories in your sources list and retrieve the missing GPG keys.
E.g. read the instructions at http://rpm.livna.org/
http://rpm.livna.org/RPM-LIVNA-GPG-KEY http://www.fedora.us/FEDORA-GPG-KEY
Ok, thank you very much, that did it. I thought I had all the keys, but obviously fedora.us-key was missing.
Still the error message is at least misleading. It says: "Package aalib-1.4.0-0.fdr.0.8.rc5.1 does not have a GPG signature"
In other words, it says the package is the problem, where it should you: hey, the Fedora.us key is missing, please import.
Should this be a bug in bugzilla? Or a feature request? (new ground to me).
Guus. -- A.J. Bonnema, Leiden The Netherlands, user #328198 (Linux Counter http://counter.li.org)