Debian Linux updating problem

While I tried to update my Debian machine I encountered key signature problem:

# apt-get update
...
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 9AA38DCD55BE302B

Solution is easy:

# gpg --keyserver wwwkeys.eu.pgp.net --recv-keys 9AA38DCD55BE302B
# gpg --export --armour 9AA38DCD55BE302B | apt-key add -