title: What is the best way to obfuscate numerical IDs in an application
body: <p>Given I've got a site where most of the resources have numerical IDs (i.e. user.id question.id etc.) but that like the Germans looking back on WWII I'd rather not reveal these to the observers, what's the best way to obfuscate them?</p>
  
  <p>I presume the method is going to involve the .to_param and then some symmetric encryption algorithm but I'm not sure what's the most efficient encryption to do and how it'll impact lookup times in the DB etc.</p>
  
  <p>Any advice from the road trodden would be much appreciated.</p>