Public blockchains have a privacy problem that is easy to forget because it is structural: the transparency that makes them auditable also makes them exposed. Every amount, every address, every transfer is visible to anyone. For a payments network handling commercial transactions, that is a non-starter — you cannot run a card business on a ledger where competitors can read your volumes.
US11151558B2, “Zero-knowledge proof payments using blockchain,” granted to American Express Travel Related Services Company on October 19, 2021, applies zero-knowledge proofs to that tension. Classified under G06Q 20/389 with H04L 9/3221 (zero-knowledge), it claims proving a payment is valid without putting the sensitive details on the ledger.
The right question to ask of any zero-knowledge claim is: what exactly does the verifier learn, and what stays hidden? The whole value is in that boundary. A well-designed payment proof convinces the network that funds exist, that the payer is authorized, and that no double-spend occurred — while revealing none of the amounts or identities a transparent chain would otherwise broadcast. The claim defines where that line is drawn.
This is a recurring and durable Amex theme, not a one-off. The same applicant line carries forward into later grants — the continuation US11748750B2 (zero-knowledge proof payments, September 2023) and the biometric identity-verification grant US11645654B2 (May 2023). Read together, they sketch a deliberate program: prove things about people and payments without exposing the underlying data.
Per the desk's rules: this is an issued grant (B2), not an application; and it is a method claim, not a deployed product. A patent on private blockchain payments does not mean Amex shipped a private blockchain — it means Amex staked the technique.
For the strategy reader, the signal is a major payments incumbent treating privacy-preserving cryptography as core IP, not a research curiosity. When the assignee is American Express and the continuation chain runs for years, the technology has graduated from interesting to defended.