title: Generate a Unique Key
body: <p>What’s the best way of generating a unique key, that can’t be guessed easily?</p>
  
  <p>I would like to create a unique key for both account activation and referral purposes, that includes a checksum to help prevent users from easily guessing other users activation or referral keys.</p>
  
  <p>Also, in PHP is it possible to create you own session key?
  If so, how would you make this unique?</p>
  
  <p>Any help is greatly appreciated.</p>