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Cryptocurrency could also solve this problem.

A "debit" card could have 1000 crypto wallets, each with $10 in them. If you want to pay $90, it forks over keys to 9 of the wallets, and they get drained by the merchant as soon as they have a connection.



> Cryptocurrency could also solve this problem.

Offline, without double spending risk? Absolutely not, or at least not without a lot of extra headaches.

For that, you'll need at least some trusted hardware (generally an antithesis to trustless crypto schemes) and/or a clever incentive system (e.g. with senders staking a multiple of their balance as collateral, and never being quite sure if receivers are really offline, or only pretending to be, ready to claim their stake once they get publicly verifiable proof of double spending).


This would be vulnerable to a double spending attack. Pretty trivially too unless I’m missing something.

If it became common I imagine it would stop being so quickly as fraud would rapidly catch up.




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