Zero-Knowledge Proof
A cryptographic method that lets one party prove they know something without revealing the underlying information.
What is ZK Proof?
A zero-knowledge proof (ZKP) is a cryptographic protocol in which one party (the prover) can convince another party (the verifier) that a statement is true, without revealing any information beyond the truth of the statement itself. The classic formulation requires three properties: completeness (a true statement can always be proved), soundness (a false statement cannot be convincingly proved), and zero-knowledge (the verifier learns nothing beyond the validity of the claim). In the blockchain context, ZK proofs — particularly ZK-SNARKs and ZK-STARKs — have two major applications. First, ZK-rollups use validity proofs to batch thousands of transactions off-chain and submit a compact cryptographic proof to Ethereum Layer 1, guaranteeing correctness without requiring each transaction to be re-executed on-chain. Second, ZK proofs enable privacy-preserving applications where users prove eligibility (e.g., they are over 18, or they own sufficient funds) without revealing the underlying data.
Example
zkSync Era is a ZK-rollup on Ethereum. When a user sends ETH on zkSync, the transaction is processed off-chain. A ZK-SNARK is generated proving that all transactions in a batch are valid. This single proof is verified by Ethereum Layer 1 in a single transaction, settling thousands of user transactions at once with mathematical certainty — and far lower gas cost than executing each transaction natively on Ethereum.
Source: Ethereum Foundation — ZK Proof