I was trying to install something or other tonight, using the (usually very simple) apt-get system on my web box, but it kept showing up with this error

There are no public key available for the following key IDs:
XXXXXXXXXX

Where the X’s are a hash/key of some description.
After some searching, The solution appears to be to import a key from a key-server (makes sense), here’s how:

# gpg --keyserver hkp://wwwkeys.eu.pgp.net --recv-keys XXXXXXXXXX
# apt-key add /root/.gnupg/pubring.gpg
# apt-get update

Substituting in the same hash/key.
Then, it just works…