We present a short survey of known notions of zero- knowledge proof systems in the interactive model and main results about these notions. We then introduce a new notion,an extension of proofs of knowledge,which we call
Proofs of Non-Zero Knowledge
, as they allow a prover to convince a verifier that he knows a secret satisfying some relation, without revealing any new information about the secret
or even the relation
that the secret satifies with the common input. We prove a number of basic results about proofs of non-zero knowledge, and, in the process, revisit previously studied protocols, described as ‘proofs of partial knowledge’, which are particular cases of proofs of non-zero knowledge.