[CentOS] Centos 5 yum update needs gpg key import

I just performed a fresh install of 64-bit Centos 5 on a system, booted 
fine, then performed a yum update, or at least tried to.  Files 
downloaded, and were about to install, when it complained that the gpg 
keys could not be found.

I ran into this about a month ago and found a web page showing the path 
locally to where the keys live, and providing rpm --import /to/the/path.

But of course now I cannot find that page.

Could someone kindly remind me the path to the keys, or simply the 
one-liner rpm to import the keys?

Thanks.

Scott