Friday, January 12, 2007

Crush or remote face

Do you know that it is possible to play crush or face remotely? I choose crush or face and the other player launches the coin… but how to check that the other does not lie? Just use mathematics razz In fact just use a function F difficult to reverse (hash function) : i.e.
  1. if I choose x and that I calculate y=f (x) and that I give you y, it is impossible for you to find x.
  2. if you choose x and x' different, it is quasi impossible that f (x) =f (x').
Let us now see how can wemake: we agree: crush corresponds to the even numbers and face the odd numbers… Thus if I choose x=346432113344662: that means that I chose crush… Now I calculate Ff(X) and I send it to you: it is impossible for you to find my x twisted, I let you launch the coin and announce me the result… To prove to you that I chose crush well, I give you x, you calculate f(x) and you can check that by calculating y=f (x) I cannot lie you: there exists only one x such as f(x) = y, if it is face… I lost: it is impossible for me to find a x' such f(x') =y. You thought that it was impossible: mathematics did it cool.

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