How make Licence Key for Mac Address to protect my php application : <p>I am  developing hotspot system using php language ,
and now I want to sell this system but how can I protect my system from be re selling by the buyer and I want to make sure that the license key is used by the right machine with right mac address ,that mean the license key can not be used more than one time. 
how can I do that  , I don't have any idea </p>
