This is a super contribution! One way you could improve this a bit is by having the generator save the key to a file, this way you never have the same file twice. Another thing would maybe be to have the user input a name (say the client wants to key registered to Billy Bob), then when the key is generated it could have something to do with the name, and when u enter it back in it checks for this.

Of course with hackers today, no amount of protection is ever enough -_-'