If during your apt activity you are getting some errors like this:
W: GPG error: http://ftp.us.debian.org etch Release: The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY 9AA38DCD55BE302B
Try to add the key from keyserver specifying the key id and you should be ok
~# gpg --keyserver pgpkeys.mit.edu --recv-key 9AA38DCD55BE302B
~# gpg -a --export 9AA38DCD55BE302B | apt-key add -
