Explain the concept of ZKP (Zero Knowledge Proofs) and its applications.
Instruction: Discuss what Zero Knowledge Proofs are, including their principles, and provide examples of their applications.
Updated
Official answer
A zero-knowledge proof lets a prover convince a verifier of a statement while hiding a private witness. The statement itself is normally public. The guarantee concerns information revealed by the proof, not secrecy of everything around the interaction.
The main properties are completeness, soundness and zero knowledge. An honest prover with a valid witness should succeed; a dishonest prover should have at most a specified small probability of convincing the verifier of a false statement, under the protocol's assumptions; and the verifier's view should be simulatable without the witness. Computational proof systems also rely on assumptions about adversarial resources.
In the two-ball illustration, the verifier secretly either swaps or does not swap distinguishable balls, then asks the prover which happened. Someone unable to distinguish them must guess the hidden choice. With independent fair challenges, success through k rounds by guessing has probability 2^−k. The verifier, rather than the prover, must control the hidden challenge. This is an intuition, not a production credential protocol.
Applications include proving possession of a valid credential or that a committed value satisfies a range. The proof must bind to trustworthy inputs: it cannot establish a person's real age from an untrusted self-assertion. Assess setup, circuit correctness, side channels and deployment assumptions separately.