title: Error updating emacs packages: Failed to download 'gnu' archive
body: <p>My <code>init.el</code> uses this to initialize packages:</p>
  
  <pre><code>(package-initialize)
  (add-to-list 'package-archives '("gnu" . "http://elpa.gnu.org/packages/"))
  (add-to-list 'package-archives '("melpa" . "http://melpa.milkbox.net/packages/"))
  (add-to-list 'package-archives '("melpa-stable" . "http://melpa-stable.milkbox.net/packages/"))
  </code></pre>
  
  <p>When I do <code>M-x package-refresh-contents</code> I get the following error: <code>Failed to download `gnu' archive.</code></p>
  
  <p><code>M-x toggle-debug-on-error</code> gives me this stacktrace:</p>
  
  <pre><code>Debugger entered--Lisp error: (error "Failed to verify signature archive-contents.sig: (\"No public key for 474F05837FBDEF9B created at 2014-09-29T07:20:03-0700 using DSA\")")
    signal(error ("Failed to verify signature archive-contents.sig: (\"No public key for 474F05837FBDEF9B created at 2014-09-29T07:20:03-0700 using DSA\")"))
    error("Failed to verify signature %s: %S" "archive-contents.sig" ("No public key for 474F05837FBDEF9B created at 2014-09-29T07:20:03-0700 using DSA"))
    package--check-signature("http://elpa.gnu.org/packages/" "archive-contents")
    package--download-one-archive(("gnu" . "http://elpa.gnu.org/packages/") "archive-contents")
  </code></pre>
  
  <p>Is this a problem with my configuration, and how would I fix it?</p>