Apt-get gives authentication warning every time

Question

Whenever I apt-get something, it warns me that it is unauthenticated. This is a new problem; it started today. When I do apt-key update, it does nothing, and apt-get update gives me this error at the end of its output:

W: GPG error: http://archive.canonical.com precise Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>
W: GPG error: http://ppa.launchpad.net precise Release: The following signatures were invalid: BADSIG 30C0868B8020F06A Launchpad PPA for arand
W: GPG error: http://ppa.launchpad.net precise Release: The following signatures were invalid: BADSIG 5C92FC592AE51AB5 Launchpad PPA for consindo
W: GPG error: http://ppa.launchpad.net precise Release: The following signatures were invalid: BADSIG 3BDAAC08614C4B38 Launchpad otto06217

Does anyone know what's happening or how to fix it? I'm running ubuntu 12.04 (precise).

Answer 1

ref: ubuntuforums.org

sudo apt-get clean
cd /var/lib/apt
sudo mv lists lists.old
sudo mkdir -p lists/partial
sudo apt-get clean
sudo apt-get update