Zero Knowledge

Zero-Knowledge Proofs: Proving Without Revealing, Separating Substance From Theatre

A zero-knowledge proof lets one party prove to another that a statement is true whilst revealing nothing beyond the truth of the statement itself: not the evidence, not the underlying data, not the working, only the fact. It sounds like a conjuring trick, and most people, hearing it described, assume it cannot be done. It can. The technique is not new. It was set out in a 1985 paper by Goldwasser, Micali and Rackoff; two of the three, Goldwasser and Micali, went on to receive the Turing Award, in 2012, for a body of work in cryptography of which this was a part. What has changed recently is practicality. Proofs that once demanded impractical amounts of computation can now be generated quickly enough for production systems, and the phrase has duly made its way from the journals onto the product brochures. That journey has not been kind to precision. What follows sets out what the technique actually offers, where it is earning its keep, and how to spot the cases where the phrase is carrying more weight than the mathematics.