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> That's wrong -- all that mailing a USB stick guarantees is that you don't have the USB stick any more, not that you didn't keep a copy of the contents. On pa
by cyphar 9y ago
> That's wrong -- all that mailing a USB stick guarantees is that you don't have the USB stick any more, not that you didn't keep a copy of the contents.
On paper, no-cloning theorem means you aren't able to make a copy of the contents. However, the obvious downside of this scheme is that it requires all coins to always remain as a qubit when stored -- otherwise you can re-generate the coin. Also you can't have more than one photon to contain said signal (maybe there's some coherence trick you can pull, but I've read several papers that have found that most quantum cryptography has been broken -- especially cryptography that depends on being able to detect measurement and no-cloning theorem).
I'm generally skeptical of quantum cryptography when it depends on physical properties of qubits to provide its security, simply because previous research has shown that claims of security are broken very soon afterwards.
- amluto 9y ago> However, the obvious downside of this scheme is that it requires all coins to always remain as a qubit when stored It requires a lot more than that. Among other things, it requires that you be unable to convert your coin to and from some classical representation. > I'm generally skeptical of quantum cryptography when it depends on physical properties of qubits to provide its security, simply because previous research has shown that claims of security are broken very soon afterwards. What do you mean by "physical properties of quits"? There are a lot of breaks of QKD, but they're breaking the implementation, not the underlying concept. What's needed is a real quantum computer that can process its incoming signal in such a way that it guarantees that the incoming qubit is really a qubit and not, say, a bright flash of light.