I've got another problem about this zero knowledge proof. The digital version doesn't make a lot of sense to me. It depends on the fact we don't have a fast integer factorization algorithm. But integer factorization is not proven to be NP-complete, and 3-coloring is NP-complete.

So isn't it possible that there is a polynomial time algorithm for integer factorization, but no polynominal time algorithm for 3-coloring, and therefore the "zero knowledge proof" actually reveals the answer?