Is there any workable way to make physical e-cash tokens? Would it basically be an Opendime?
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Need a convenient way to determine a coin you’ve been handed hasn’t already been redeemed/moved out of the mint.
Ecash mints need to periodically rotate the private keys they use to sign ecash so every ecash opendime would have an expiration date. Also, consider you are loading custodial bitcoin IOUs onto hardware, so there's no guarantee it will still be valid when you go to spend. There is also no way to audit the ecash on the device, so you have to spend it to validate it. I think the tech is just not suited for this use case. Better to load bitcoin onto physical hardware: it never expires, is trustless, non-custodial, easily audited.
Further reading: https://gist.github.com/callebtc/ed5228d1d8cbaade0104db5d1cf63939
Great question!
Thanks! Do federated e-cash mints also rotate keys? Maybe a federation would also give someone more confidence that an IOU handed over via Opendime would be valid for longer.
Yes. All ecash mints need to rotate their signing keys to prevent the spent ecash database from growing indefinitely.
Also, yes, that's the whole idea of a federation. It's like a hundred times harder to build than a single key system but worth it because fedimint allows you to distribute trust. As Satoshi taught us: "The root problem with conventional currency is all the trust that's required to make it work."