Zero-knowledge proofs can be generalized to a wide range of information. In fact, it turns out that any mathematical theorem with a proof can have a zero-knowledge "proof of the proof." That is, Alice can claim to have a proof of theorem T, but not wish to state it (she wants to wait for publication). Nonetheless, Alice can prove that she has proved T without revealing the proof. This very general fact is broad enough to cover specific cases like factoring large numbers and the like, which are involved in many cryptographic algorithms. The broadest scope exceeds this tutorial; we will just look at one case (others are similar in form).