The full abstract, detailed description, and claims for this granted patent are available on its official Google Patents record.
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Imagine the door and your phone both running the exact same dice machine, started from the same seed. Every time you show up, each side independently rolls the next number, and the door opens only if your number matches what it just rolled too. The actual key is never sent through the air, each side computes it from the time, a record number, and shared randomness. So a hacker who records today's code gets nothing tomorrow, because both machines have already rolled past it.
Technology areas where this patented method may apply.