title: Simple way to encrpyt/decrypt a number
body: <p>I need to encrypt a 2-digit number in a simple way. The samples I found in google seems to be quite complex. Is there any easy way to achieve that?</p>
  
  <p><strong>UPDATE</strong></p>
  
  <p>I'm working on a custom numeric captcha for my ASP.NET MVC application. I've created a custom html helper that will render an image tag with base-64 encoded string of the captcha image. The captcha image will be something like <code>23 + 12 = ?</code>. When the user submit the answer I want to validate it right? I'm not interested in storing the sum in session so I thought of encrypt the sum and attach as a hidden field and so when the user submit the form I can easily do the validation.</p>