Thread

1. piratejon · 1789617453 · focus · HN ↗

   That's really neat! Seems potentially adaptable to paper currency--a verifiable QR code digital signature of the bill's serial number creates a cryptographically hard obstacle to counterfeiting!

   1. kqp · 1789618336 · focus · HN ↗

      Copy known good serial number + signature.

      1. teravor · 1789620497 · focus · HN ↗

         combine with a central authority server network and make it blind signatures and you have untraceable e-cash.

         1. mitxela · 1789627417 · focus · HN ↗

            No government wants untraceable e-cash. They want it fully traceable.

            1. teravor · 1789651688 · focus · HN ↗

               it would depend on the government and the situation. I suspect most don't realize this is possible. a small government can generate immediate demand for their currency doing this.

               1. lxgr · 1789654005 · focus · HN ↗

                  The original e-cash paper is from 1983. Governments absolutely know this is possible.

                  It's just much "too private" to get any political traction. At the very least, I suspect an acceptable modern alternative would either have caps on what can be sent/received completely anonymously (e.g. per recipient and timespan) or want non-anonymous recipients (to allow for VAT/sales tax accounting etc.)

         2. lxgr · 1789627839 · focus · HN ↗

            Blind signatures don’t work like that. Once you unblind them, they are very traceable. Chaumian e-cash can only be spent once for that reason.

            1. teravor · 1789651336 · focus · HN ↗

               when you unblind a blind signature all the signer knows is that it's a signature they signed at some point, they know nothing (true zero knowledge) about when or where they signed it among all the other signatures.

               1. lxgr · 1789653799 · focus · HN ↗

                  Yes, and then you have a signed piece of data that others can verify. How does that help you with preventing duplication of signatures?

                  E-cash depends on the secrecy of the signed data, and immediate redemption with the issuer once it's been spent/accepted. This is a terrible model for physical cash.

                  1. teravor · 1789656532 · focus · HN ↗

                         > immediate redemption with the issuer once it's been spent/accepted. This is a terrible model for physical cash
                     
                     

                     not when everything is now online.

                     also the obvious way such cash would work is that "redemption" is just the new minting of coin. the central authority will mint a new coin by blindly signing your secret after you "destroy" the spent coin by giving them the unblinded signature.

                     1. lxgr · 1789657383 · focus · HN ↗

                        This thread is about printing QR codes on physical cash. GGP explicitly said:

                        > That's really neat! Seems potentially adaptable to paper currency--a verifiable QR code digital signature of the bill's serial number creates a cryptographically hard obstacle to counterfeiting!

                        I don't see how any e-cash solutions can help here.

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