Since Debian’s 0.6 version of apt package signatures have been checked. Adding a new repository source e.g.
deb http://packages.kirya.net/debian/ sid main contrib non-free
to your /etc/apt/sources.list file and running the command apt-get update you would most probably get the following error in the output :
W: GPG error: http://packages.kirya.net sid Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY EEFB43B2FBABB737
W: You may want to run apt-get update to correct these problems
Now the repositories website is the first place I would look for instructions to import the key, if this is not an option I would try this :
Required Packages:
apt-get install debian-archive-keyring apt-key
run as root(or use sudo):
sudo gpg --keyserver hkp://wwwkeys.eu.pgp.net --recv-keys EEFB43B2FBABB737
this gave me:
gpg: requesting key FBABB737 from hkp server wwwkeys.eu.pgp.net
use the key from the output to run:
sudo gpg --armor --export FBABB737 | sudo apt-key add -
If all goes well output should be: OK
Now run
apt-get update
and enjoy the new repository 
I’m not sure how correct this method is but so far for me it has worked without any issues.