title: Scrambling Social Security Number
body: <p>I'm working with a data set that deals with personal data (i.e. data that deals with people, not [necessarily] private data)... This data that changes over time, and the format is imposed by the client. I need something to use as a primary key, and unfortunately the only field that uniquely identifies a person and doesn't change unpredictably is SSN. The ID number (primary key) is going to be public facing, so I can't publish that, but I'm hoping to obscure it.</p>
  
  <ul>
  <li>The result must be numeric.</li>
  <li>The result may be up to 25 digits long.</li>
  <li>The result must be unique.</li>
  <li>The result should be as difficult as possible to reverse without a key, given the constraints above.</li>
  </ul>
  
  <p>Is there a numeric cipher that would fit this?</p>
  
  <p>Am I crazy for trying this?</p>