Normally the Debian software distribution and upgrade process is fantastic. An occasional aptitude update; aptitude dist-upgrade and my systems are all up to date. But Debian updates keys once a year and their key distribution process is not entirely smooth. The end result is an error like one of these
aptitude — debian WARNING: untrusted versions of the following packages will be installed
apt-get — The following packages cannot be authenticated
You can just ignore these errors, upgrade anyway, and hope for the best. But a better solution is to manually install the 2006 key first, then re-run the update.
apt-key add ziyi_key_2006.asc
aptitude update
aptitude dist-upgrade
I'm still not sure how to verify you really got the right 2006 key, I decided to chance it. Now would be the perfect time to h4x0r shudder.

There's background info on the Debian Wiki.
  2006-01-11 01:56 Z