title: ssl/tls hanshake:: NIST Special Publication 800-52 Revision 1
body: <p>Can someone explain the contradictions in the BOLD text below from the NIST document.</p>
  
  <p>"The handshake protocol is <strong><em>used to optionally exchange X.509</em></strong> public key certificates (5) to authenticate the server and the client to each other. In order to comply with these guidelines, <strong><em>the server always presents an X.509 public key certificate</em></strong> that complies.........."</p>
  
  <p>(4). In these guidelines, “change cipher spec” refers to a protocol, and “ChangeCipherSpec” refers to the message used in that protocol.
  (5). The use of <strong><em>X.509 public key certificates is fundamental to TLS</em></strong>. For a comprehensive explanation of X.509 public key certificates see [Adams99] or [Housley01]. In these guidelines, the terms “certificate” and “public key certificate” are used interchangeably.</p>