Proof of knowledge

A witness is the information satisfying a verifiable statement: a secret, a signature or a solution to a computation. Knowledge soundness requires that an accepted proof imply possession of that witness under the protocol’s security model.

Knowledge and zero knowledge answer different questions. The former concerns what the prover knows; the latter concerns what the verifier learns. A proof can have one property without the other. SNARK denotes a succinct, non-interactive argument of knowledge; the zk prefix adds zero knowledge.

Proofs of knowledge can support authentication or demonstrate computation. Privacy, trusted-parameter requirements and proving and verification costs depend on the construction.