title: Secure usage of SHA512
body: <p>I have a question about the security of the following usage of SHA512:</p>
  
  <p>If I have two strings, <strong>x</strong> and <strong>y</strong>.
  Is it possible to derive SHA( <strong>x</strong> ) and SHA( <strong>y</strong> ) from SHA( <strong>x+y</strong> ) or reversed? 
  <strong>x+y</strong> is string <strong>x</strong> concatenated with <strong>y</strong>.</p>
  
  <p>Thanks in advance!</p>