Comment 3 for bug 1054648

Hello,

You should check out this AskUbuntu thread for possible solutions: http://askubuntu.com/questions/1877/what-is-the-easiest-way-to-resolve-apt-get-badsig-gpg-errors

If I had to guess, I would say that following solution from the link above might work (the second post modified to work with direct copy pasting):
sudo mv /var/lib/apt/lists /var/lib/apt/lists.old
sudo mkdir -p /var/lib/apt/lists/partial/
sudo apt-get update

Hope this helps.