Zero-knowledge proof

A zero-knowledge proof is a way to prove that something is true without revealing the underlying data that makes it true. This matters because it lets blockchains verify transactions or identity claims while keeping the private details hidden, which cuts down what gets exposed on a public ledger. For example, a zk-rollup like zkSync can bundle thousands of transactions and submit a single proof to Ethereum confirming they're all valid, without showing each sender, receiver, or amount on-chain. The same idea lets someone prove they're over 18 without sharing a birth date, or prove they hold enough funds without revealing their balance. It's the math behind privacy coins like Zcash and a growing chunk of Ethereum's scaling roadmap.