Failed package verification

[John Scott]

Since my upgrade to Kubuntu 13.10, I've been getting a warning every 
time the software updater runs that the packages can't be authenticated. 
I get complaints about missing repository keys. I've looked up articles 
about adding the keys but can't find one that explains how to add keys 
without assuming too much. It assumes either you have the keys already, 
or that you know which key you need, or what url you should use, etc. I 
would have expected this to be readily available in a conspicuous faq 
but to no avail.

Can someone explain how to get the key for the root distro and also 
updates, assuming it has a different key? I saw a command for apt-key:
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys KEY
but like every article I find it has a variable "KEY" code which it says 
I can get from apt-get output. I think this code is the one thing I 
don't get from apt-get. I don't know why the upgrade from 12.10 failed 
to update the keys but it did. I've never had this problem after an 
update before but I've had apt-get problems constantly on 13.10.

Regards,

John Scott