Interesting analogy. Your last paragraph seems to be missing some line breaks though (and would look better if you used the HTML <ul> and <li> tags rather than a "handmade" list). I'd also go into trying to explain, after that last paragraph, why it's impossible to forge and steal things - just simple explanations like "because you need x information to do so, and if you don't have it, calculating it would take trillions of years".