title: Emacs: Failed to verify signature archive-contents.sig
body: <p>Recently tried to update emacs packages and got this.</p>
  
  <pre><code>Failed to verify signature archive-contents.sig:
  No public key for 066DAFCB81E42C40 created at 2019-10-02T10:10:02+0100 using RSA
  Command output:
  gpg: Signature made Wed 02 Oct 2019 10:10:02 AM BST
  gpg:                using RSA key C433554766D3DDC64221BFAA066DAFCB81E42C40
  gpg: Can't check signature: No public key
  </code></pre>
  
  <p>Any ideas why?</p>