A zero-knowledge proof (ZK-proof) is a cryptographic technique that enables one party (the prover) to demonstrate to another party (the verifier) that a statement is true without revealing any information beyond the validity of the statement itself. This concept is one of the most important innovations in blockchain technology and cryptography.
In simple terms, a ZK-proof answers the question: "Can I prove that I know something without telling you what I know?" For example, you could prove you have enough funds to complete a transaction without disclosing your actual balance.
There are two main types of zero-knowledge proofs used in blockchain:
- ZK-SNARKs (Succinct Non-Interactive Arguments of Knowledge) — compact proofs that are fast to verify but require a trusted setup ceremony. Used by Zcash and many ZK rollups.
- ZK-STARKs (Scalable Transparent Arguments of Knowledge) — larger proofs that do not require a trusted setup, offering greater transparency. Used by StarkNet.
ZK-proofs have two major applications in crypto:
- Privacy — enabling confidential transactions where amounts and addresses are hidden, as in Zcash.
- Scalability — ZK-rollups bundle thousands of transactions off-chain and submit a single proof to the main chain, dramatically increasing throughput while maintaining the security of the base layer like Ethereum.
Major ZK-rollup projects include zkSync, StarkNet, Polygon zkEVM, and Scroll. These networks are at the forefront of Ethereum scaling and are expected to play a central role in the future of blockchain infrastructure alongside other solutions like sidechains.