title: How does a cryptographically secure random number generator work?
body: <p>I understand how standard random number generators work. But when working with crytpography, the random numbers really have to be random. </p>
  
  <p>I know there are instruments that read <a href="http://en.wikipedia.org/wiki/Hardware_random_number_generator" rel="noreferrer">cosmic white noise</a> to help generate secure hashes, but your standard PC doesn't have this. </p>
  
  <p>How does a cryptographically secure random number generator  get its values with no repeatable patterns?</p>