zk-SNARK
Zero-Knowledge Succinct Non-interactive ARgument of Knowledge — compresses a computation proof to ~200 bytes that verifies in milliseconds, regardless of problem size.
Built on pairing-based cryptography (BLS12-381). Requires a trusted setup (a ceremony where participants jointly generate parameters; one honest participant suffices). Groth16 is the classic SNARK; newer PLONK and Halo2 have universal or no setup.
Powers Zcash, Tornado Cash, Polygon zkEVM, Scroll, Aleo. Slow proof generation (seconds to minutes), fast verification — perfect for on-chain validation of off-chain compute. zk-STARK is a post-quantum-safe variant without a trusted setup but with larger proofs.