The question that makes zero-knowledge proofs sound impossible how can I prove I know a secret without telling you the secret? Yet it is one of the deepest results in modern cryptography, and it is increasingly practical. The intuition cryptographers use is a cave with a looped passage and a locked door; you can convince a skeptic you know the door's password by repeatedly emerging from whichever side they shout, without ever speaking the password. Enough rounds and the only explanation is that you really know it.
American Express stakes a practical version of this in US11151558B2, "Zero-knowledge proof payments using blockchain" (issued October 2021, classified under H04L 9/3218 — the CPC subclass for zero-knowledge protocols). The claim describes validating a payment on a blockchain using a zero-knowledge proof, so the network can confirm the transaction is legitimate — the payer has the funds, the rules are followed — without the transaction details being exposed to every participant.
The way this actually works in a payment context the payer constructs a proof that the transaction satisfies the required conditions (sufficient balance, valid signature, no double-spend) and publishes only that proof. Validators check the proof and learn one bit truth or falsehood. They do not learn the amount, the balance, or the parties beyond what is strictly necessary. On a public ledger, where everything is otherwise visible to everyone, that selective disclosure is the entire value proposition.
This is a family, and the continuation matters. US12093948B2 (September 2024) carries the same title and inventors forward, which on this desk reads as a sign American Express is maintaining and extending the position rather than letting a single grant sit. A maintained family is a stronger strategic signal than one isolated patent.
Zero-knowledge proofs are not only for payments, and a second grant shows the breadth. IDEMIA's US11032079B2 ("Verification method of biometric authentication," 2021) uses zero-knowledge techniques so a biometric can be verified without the raw template being exposed — proving "this is the right fingerprint" without handing over the fingerprint. Same primitive, different stakes prove the match, reveal nothing else.
Why it matters: the demand for privacy-preserving verification — paying, proving identity, proving age or eligibility — is exactly where regulation and user expectation are converging. Zero-knowledge proofs are the cryptographic tool that satisfies both, and the granted claims here show financial and identity players staking concrete applications of it, dated and classified under H04L 9/3218.