Verify foreign Elastic IP

Hello everyone, as a software vendor deploying licensed tools, we would ask our customers to send us an elastic ip (eip) or a MAC address from an elastic network interface (eni), in order to have a **permanent **basis for our license keys.

Now, in order to avoid unnecessary re-issuing new license keys, how can I verify, that the IP or the MAC address from the customer is really an elastic ip or eni?