zkSNARK

zkSNARK stands for zero-knowledge succinct non-interactive argument of knowledge. It is a zero-knowledge proof in which a prover can convince a verifier that a statement is true without revealing the witness, while the proof is short and quickly verifiable. The non-interactive property means that, after a single common reference string is published, the proof can be checked without back-and-forth communication. Succinctness refers to proofs whose size and verification time scale cheaply with the complexity of the statement.

How it works: a computation is encoded as a circuit or algebraic constraint. A trusted setup generates a common reference string (CRS) for that circuit. The prover uses a witness to produce a short proof from the CRS. The verifier uses the CRS and the public inputs to check the proof efficiently, with verification time largely independent of the circuit size.

Groth16 is a widely used zkSNARK construction known for very small proofs and fast verification, but it requires a trusted setup. Other variants seek to remove or minimize trusted setup or to achieve post-quantum security.

In practice, zkSNARKs are used to enable private or scalable computations in blockchains, most famously for shielded transactions in Zcash and for privacy-preserving or scalable smart contracts in other systems. They continue to be developed with attention to security, trust assumptions, and the implications of quantum attacks.