Explaining Zero Knowledge to your children

[hallam at w3.org]

The cave analogy sucks.

The way I tried to explain Zero Knowledge is this:


Imagine that you have a duplicator device which you want to sell, you don't
want to explain why it works to the buyer however since then they would 
just make their own (patents have been abolished by this time). You also don't 
want the buyer to be able to prove to anyone else that you have a duplicator.

So what you do is you play the "what hand is it in game" and you do this with a 
10$ bill provided by the buyer and who records its serial number. You hold the 
original article in one hand and the duplicate in the other. The buyer choses 
one hand, you show the article in that hand. The buyer knows you had a 50:50 
chance of a lucky guess so you do it again, each time the probability of getting 
it right by a lucky guess halves. After 10 tries or so it is virtually certain 
that you were not faking.


Any better ideas...

	Phill