Depends:
# apt-get install debian-keyring debian-archive-keyring
# apt-get install debian-keyring debian-archive-keyring
If you get o follow error from an unofficial repository:
W: GPG error: ftp://ftp.ragner.net etch Release: The following
signatures couldn't be verified because the public key is not available:
NO_PUBKEY 08GC463D1F41D098
Take the GPG key
# gpg --keyserver subkeys.pgp.net --recv-keys 08GC463D1F41D098
and add to apt
gpg --export --armor 08GC463D1F41D098 | sudo apt-key add -
End