A zero-knowledge(zk) proof lets a prover convince anyone that some statement is true while keeping secret how or why the statement is true.

The first mainstream uses of zero-knowledge proofs were for private payments in blockchains like Zcash and then for scalability of blockchains in general. In both settings, we hide data to improve privacy or reduce blockchain validation costs. But private payments, unfortunately, have seen limited direct demand. And while blockchain scalability needs faster proofs, these proofs need not even be zero-knowledge, merely succinct. What are practical zk proofs good for? This talk considers zk proofs + blockchains as a tool both for cryptocurrency and broader applications.