title: Scratch card number & serial generator
body: <p>In a company, We need to make scratch cards similar to the ones available in the market.</p>
  
  <ul>
  <li>there is number hidden which needs to be scratched.</li>
  <li>Serial number which is visible.</li>
  </ul>
  
  <p>My question is very basic that how do other companies make those hidden and serial numbers. I have read little bit about hashing but couldn't connect the dots. </p>
  
  <ol>
  <li>Is the serial number independent of the invisible part?</li>
  <li>Do they take a serial number and hash that to make the invisible part or vice versa?</li>
  </ol>
  
  <p>and also,</p>
  
  <ol>
  <li>How are invisible numbers made? like what algorithm is commonly used for that?</li>
  </ol>
  
  <p>Any insight will be helpful. Thank you.</p>