apt-get update may give you the following error

 

W: GPG error: http://ftp.de.debian.org squeeze Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY AED4B06F473041FA
W: GPG error: http://security.debian.org squeeze/updates Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY AED4B06F473041FAthe solution is to update the debian keyrings - root issue is that you (me) haven't updated them during a full update from lenny to squeeze.

I'm not yet sure, the following is supposed to work ,but it didnt. 

apt-get upgrade debian-archive-keyring && apt-get dist-upgrade

The downside is that it will often by dependency turn into yet another apt-get upgrade. But thats what we came for, right?

Documentation seems to exist at:http://wiki.debian.org/SecureApt

 

Proxy issues

One thing which can cause you to get stuck real bad here:

The keyring stuff uses GNUtls.

GNUtls doesn't read the apt proxy setitngs!

GNUtls doesn't read $HTTP_PROXY

GNUtls doesn't read $HTTPS_PROXY.

 

It only reads $http_proxy and $https_proxy !!!

Try adjusting that and...