There should be a wallet app that can generate digital paper wallets on cellphone of specific amounts.
Customer just need to show that QR code (Private key) to retailers webcam and it should sweep funds.
ie:
1.Retailer tells customer to pay 55.5$
2.Customer generates a QR code for 55.5$ on his cell and shows that on retailers webcam/machine
3.Retailers App scans it via webcam and sweep's all funds to a new private key.
This way, there will be no double spend possible.
Very nice. Does anything support this at the moment?
Surely in this scenario one could still execute a double spend attack, but with different parties: if the customer also used the private key at the same time it would be the customer's payment verses the retailer's payment and who's ended up on the longest blockchain?
Well this issue can be solved if Customers App will be customized to delete privatekey/QR code after single use (once it checks that there is a unconfirmed transaction output)
Or
App should generate a encrypted QR code ( Private key+ encryption) or just simply a "coupon" that can be decrypted/accepted by Retailers app only.
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