Zero-knowledge proof (ZK proof)

A zero-knowledge proof is a cryptographic method that lets one party prove a statement is true without revealing any information beyond the fact that it is true. For example, you could prove you are over 18 without revealing your date of birth, or prove a batch of transactions is valid without the verifier re-running them.

The idea was first described by researchers Shafi Goldwasser, Silvio Micali and Charles Rackoff in the 1980s. In crypto it has two big uses. The first is privacy: Zcash uses ZK proofs (zk-SNARKs) to allow shielded transactions that hide sender, receiver and amount. The second is scaling: ZK rollups generate a proof that thousands of transactions were executed correctly, and the base chain only needs to check the short proof.

Generating proofs is computationally heavy, but the technology has improved quickly. Terms you will see include zk-SNARKs, zk-STARKs and zkEVMs, which are rollups compatible with Ethereum's virtual machine.