Su suggerimento di @Ospizio.

In questo articolo del New Yorker si spiega, tra indovinelli e problemi di fisica, come sia possibile implementare una tecnica per il disarmo nucleare senza rivelare segreti militari agli eserciti avversari.

“Trust, but verify.” It is a translation of a Russian proverb, and Reagan used it often in his dealings with the Soviet Union over nuclear disarmament, as both countries chipped away tentatively at their Cold War stockpiles. For him, the saying encapsulated the idea that a good treaty would require rigorous inspections, to insure that neither side was dragging its feet or, worse, disposing of decoy bombs, rather than real ones. But how should the process of verification work?

[…]

Suppose that you and a friend are standing in front of a pine tree. Your friend claims to have a quick way of knowing how many needles are on it—several hundred thousand, say—but doesn’t want to reveal either the exact number of needles or his method of counting. To test whether he’s being truthful, you have the friend privately count all the needles on the tree, and then you take a handful of needles and tally them up, keeping the total to yourself. Your friend counts the needles on the tree again, then tells you the difference between the first and second numbers. If he really does know how many needles are on the tree, then he also knows how many are in your hand. He has proved he wasn’t bluffing, but at the same time he has avoided divulging anything new to you. And there is no plausible way your friend could fake the result, other than just guessing, which would be easily ferreted out if you played the game a few times in succession with different handfuls of needles. In the cryptologic jargon, the proof is both complete (proving positive knowledge) and sound (cheating is detectable).

 

Immagine CC BY 2.0 di TVA da flickr