I am about to implement a very basic licensing feature for my application. A serial number may be granted per-machine (or per-operating-system) or per-user (as for CAL in Windows Server: if my application is used by several users on one machine or if it is used by one user on several machines).

1. For per-operating-system licensing, I use SerialNumber of Win32_OperatingSystem.

2. For per-user licensing, I use:

   WindowsIdentity currentIdentity = WindowsIdentity.GetCurrent();
   if (currentIdentity != null)
   {
       SecurityIdentifier userSid = currentIdentity.User.AccountDomainSid;
       Console.WriteLine(userSid);
   }
   

A hash of an obtained OS serial number or SID is then stored in the database, associated with application serial; each time the program starts, it queries the server, sending hash of OS SN/SID and application serial.

Is it a right thing to do it or is it completely wrong? Will it work on every Windows machine? (For example, using motherboard serial is wrong)