packages cannot be authenticated

["John Biederstedt" <john@johnsdomain.org>]

Hi
When installing packages with apt-get, I get the message "WARNING: The
following packages cannot be authenticated!".  I installed the key from
http://ftp-master.debian.org/ziyi_key_2006.asc into root's (and my own)
keyring with 

# cat ziyi_key_2006.asc | gpg --import

I then put the key into apt-key with 

# gpg --export -a 2D230C5F | apt-key add -
OK

I still see the "WARNING: The following packages cannot be
authenticated!" message when installing or updating a package, such as 

$ sudo apt-get --reinstall install sudo
Reading package lists... Done
Building dependency tree... Done
0 upgraded, 0 newly installed, 1 reinstalled, 0 to remove and 2 not
upgraded.
Need to get 0B/162kB of archives.
After unpacking 0B of additional disk space will be used.
Do you want to continue [Y/n]? y
WARNING: The following packages cannot be authenticated!
  sudo
Install these packages without verification [y/N]? n
E: Some packages could not be authenticated

Am I missing something obvious?  Or is something wrong with how I've put
the kew key into apt-key?

Any info is greatly appreciated!