zkSNARKs

zkSNARKs are a class of cryptographic proof systems that allow a prover to convince a verifier that a secret witness satisfying a computation exists, without revealing the witness, and with a proof that is short and quick to verify. The acronym stands for zero-knowledge Succinct Non-Interactive Argument of Knowledge. They are zero-knowledge, meaning no information about the witness leaks; succinct, yielding small proofs and fast verification; non-interactive, requiring only a public setup to check proofs; and an argument of knowledge, meaning a valid witness is presumed to exist for the statement.

In practice, the computation is encoded as a circuit or algebraic constraint system. A trusted setup produces a proving key and a verification key. The prover uses the witness and the proving key to generate a short proof; the verifier uses the verification key to validate the proof in time largely independent of the circuit size.

zkSNARKs enable privacy-preserving applications such as shielded transactions in blockchains (for example, Zcash) and verifiable outsourced computation. They are also used in privacy-preserving identity and data processing. The main advantage is small proofs and fast verification, which reduces on-chain data and bandwidth needs.

Limitations include the need for a trusted setup in most constructions; a setup compromise can undermine security. Circuit design and proving can be computationally intensive, and some schemes rely on elliptic-curve assumptions that may be vulnerable to quantum attacks. Researchers are exploring transparent SNARKs and post-quantum variants, but these approaches involve trade-offs.