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Consider one scenario that some envisage in an IoT world, where a self-driving car that needs to get somewhere in a hurry can make a small payment to another self-driving car to let it pass. As discussed, you’ll need a distributed trust system to verify the integrity of the transaction, which may involve a lot more information than just that of the money transfer before it can be processed—for example, you may need to know whether the overtaking car is certified as safe to drive at the faster speed, or whether one car’s software can be trusted not to infect the other with malware. These kinds of verifications, as well as that of the fund balance in the paying car’s wallet, could be run through a blockchain log to check the validity of each side’s claims, giving each the assurances they need without having to rely on some certifying central authority. The question, though, is: would this transaction be easily processed if it were based on a private blockchain? What are the chances, in a country of more than 230 million cars, that both vehicles would belong to the same closed network run by a group of permissioned validating computers? If they weren’t part of the same network, the payment couldn’t go through as the respective software would not be interoperable. Other car manufacturers might not want to use a permissioned verification system for which, say, GM, or Ford, is the gatekeeper. And if they instead formed a consortium of carmakers to run the system, would their collective control over this all-important data network create a barrier to entry for newer, startup carmakers? Would it effectively become a competition-killing oligopoly? A truly decentralized, permissionless system could be a way around this “walled-garden” problem of siloed technology. A decentralized, permissionless system means any device can participate in the network yet still give everyone confidence in the integrity of the data, of the devices, and of the value being transacted. A permissionless system would create a much more fluid, expansive Internet of Things network that’s not beholden to the say-so and fees of powerful gatekeepers.
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Michael J. Casey (The Truth Machine: The Blockchain and the Future of Everything)