title: Trust Levels in user's device
body: <p>I am creating a PHP/MySql application and for some reasons I have to establish a Security/Trust relationship between the user's device and my system. The following shows my options and shortcoming:</p>
  
  <p><strong>Cookies:</strong> This method of sustaining an existing relationship was the first to mind, but could easily be erased by the user of the device. </p>
  
  <p><strong>User Agent String:</strong> This can be spoofed and proven unreliable.</p>
  
  <p><strong>MAC Address:</strong> Same reason as the user agent. This option cannot be trusted.</p>
  
  <p><strong>IP Address:</strong> This for me is a no no especially for users with dynamic IP's or NAT </p>
  
  <p>Would appreciate anyone with an answer to my idea. I am proficient in PHP/MySql so applying the logic shouldn't be a problem</p>
  
  <p>Thanks in advance</p>