title: Jenkins: signature verification failed in update site 'default' (show details)
body: <p>I have installed Jenkins on <code>Amazon EC2</code> instance and I am trying to get an updated list of available plugins.<br>
  When I go to <code>Manage Plugins --&gt; Advanced --&gt; Check now(at the bottom)</code>, I get an error as below:  </p>
  
  <blockquote>
    <p>signature verification failed in update site 'default' (show details)</p>
  </blockquote>