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!

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kqp 5 hours ago | parent | next [-]

Copy known good serial number + signature.

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teravor 5 hours ago | parent [-]

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

	▲	lxgr 3 hours ago \| parent \| next [-]
		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.
	▲	mitxela 3 hours ago \| parent \| prev [-]
		No government wants untraceable e-cash. They want it fully traceable.

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lxgr 3 hours ago | parent | prev [-]

It’s a bunch of static signed data, which is hard to modify but trivial to copy. Not exactly what you’d want for bank notes.

NFC and a challenge-response protocol could work, though, like e.g. the one used in biometric passports.