Fusing physics, cryptography to solve a nuclear inspection paradox

The solution to ridding nations of nuclear warheads may come from a simple puzzle involving marbles.

That, at least, is what lies at the core of a warhead verification protocol designed by a Princeton University team, published this week in the journal Nature.

Physicist Alexander Glaser, who has one foot in the public policy school and the other in the engineering faculty at Princeton, was puzzling over an apparent paradox: How can you authenticate something without revealing anything about it? After all, nobody wants a foreign inspector seeing how a warhead is made.

The standard answer thus far has been to design an electronic gizmo to mask the classified information but still spit out a yes/no answer. Such information screens, however, could be hacked.

Glaser happened to vent his frustration to the right people: mathematicians who tinkered with zero-knowledge proofs.

I said, the challenge is to do it without learning anything, and they said, what about what we call zero-knowledge proofs?

Glaser hadnt heard of such a thing. He reached out to Boaz Barak, a former Princeton associate professor working for MicrosoftResearch, and fellow Princeton plasma physicist Robert Goldston. The trio set out to take zero-knowledge proofs into the nuclear age.

Personally, I just find its a fascinating and counterintuitive statement, that I can prove something is true without revealing why something is true, said Glaser.

A classic zero-knowledge proof involves a secretive marble owner. He has two cups holding the same number of marbles, between 1 and 100, and wants to prove they are equal. But he doesnt want to pour out the marbles for counting. So, the secretive marble owner strikes a deal: Hell prepare two buckets, each holding 100 marbles minus the number of marbles he has in each cup, and then allow an inspector to randomly match an unseen cup and an unseen bucket.

The owner then pours the contents of the chosen cup into the chosen bucket, and hands over the bucket for counting. It should add up to 100. So should the other bucket with the other cup's contents.The inspector has verified what the marble hoarder claimed, but still does not know how many marbles he had.

More here:
Fusing physics, cryptography to solve a nuclear inspection paradox