title: service_identity installed but not working
body: <p>under root I ran <code>pip3 install service_identity</code> and <code>easy_install service_identity</code></p>
  
  <p>both installed successfully yet the warning still shows and clients can't connect.
  They close before handshake.</p>
  
  <p><strong><em>Full Warning</em></strong></p>
  
  <blockquote>
    <p>:0: UserWarning: You do not have a working installation of the service_identity >module: 'No module named 'cryptography.x509''.  Please install it from <a href="https://pypi.python.org/pypi/service_identity" rel="nofollow noreferrer">https://pypi.python.org/pypi/service_identity</a> and make sure all of its >dependencies are satisfied.  Without the service_identity module, Twisted can >perform only rudimentary TLS client hostname verification.  Many valid >certificate/hostname mappings may be rejected.</p>
  </blockquote>