Unforgeable Quantum Tokens Delivered over Fiber Network
spectrum.ieee.org
spectrum.ieee.org
https://www.nec.com/en/press/202411/global_20241118_01.html
And it has goodies like:
> Token: A digital certificate indicating certain rights and values, such as digital assets, user information, and access rights.
That is not much detail.
> Quantum key distribution (QKD) systems use quantum mechanics to share random secret keys between two communicating parties in order to guarantee secure communication, and then encrypt and decrypt information based on those keys. (Patented (as of November 18, 2024))
This sounds like rather old technology. What exactly is novel here?
In any case, the article’s drawing makes it look like the customer’s “token” is some classical information. This cannot work.
(This is a thing I am fine with, research is research and it doesn't necessarily need a near-term practical outcome, but why is it "sold" to the public as though there is some useful capability coming just around the corner?).
Who would use dedicated fiber to get secrets between point A and point B? Am I just insufficiently imaginative?
Whenever I read these headlines I am reminded of how much biological research needs to have a "could one day cure cancer" to give funders and journalists a hook.
Cloud providers also have some dedicated fiber between their data centers.
If the computers are secure they can presumably do authenticated key agreement perfectly well and if they are not then I don't see how the QKD helps.
Security is nuanced and thinking in binaries is often a mistake - but I don't see how QKD meaningfully changes anyone's threat model in any plausible deployment scenario.
(Of course, one can also augment DH with symmetric crypto for the datacenter use case, with someone trustworthy literally carrying the key to the other end of the link, and I see no realistic usage of QKD that will outperform that unless one is worried about post-compromise recovery of a symmetric key stored in a piece of hardware. Plus, QKD has its own issues: security of QKD is subject to catastrophic failures if the single-photon source isn’t actually a single-photon source and possibly also if a malicious light source injected into the fiber causes the transmitter to stop being a single-photon source or the receiver to behave in a manner inconsistent with any possible single received photon. Think of these as side channel and fault attacks that are rather difficult to manage.)
Whilst theoretically they are secure, I worry about potential huge side-channels allowing leaking of the key...
All it takes is a few extra photons emitted at some harmonic frequency for the key to be leaked...
I would much prefer dumb hardware and clever digital software, because at least software is much easier to secure against side channels, and much easier to audit.
That said, wherever you convert the quantum data into classical data there will be potential side channels. For example, there have been attacks based on using a laser down the communication line to track the orientation of the measurement device at the receiver.
In general, the more you can do while the data stays quantum the better. For example, if you transduce the photon into a qubit inside a quantum computer, then the measurement can be hidden away inside the computer, instead of exposed to the communication line. And the measurement basis can be chosen after transmission arrival, instead of before.
[1] https://onlinelibrary.wiley.com/doi/full/10.1002/qute.202300...
How does photonic phase state collapse due to fiber mitm compare to a heartbeat on a classical fiber?
There is quantum counterfactual communication without entanglement FWIU? And there's a difference between QND "Quantum Non-Demolition" and "Interaction-free measurement"
From https://news.ycombinator.com/item?id=41480957#41533965 :
>> IIRC I read on Wikipedia one day that Bell's actually says there's like a 60% error rate?(!)
> That was probably the "Bell test" article, which - IIUC - does indeed indicate that if you can read 62% of the photons you are likely to find a loophole-free violation
> [ "Violation of Bell inequality by photon scattering on a two-level emitter", ]
Bell test > Detection loophole: https://en.wikipedia.org/wiki/Bell_test#Detection_loophole :
> when using a maximally entangled state and the CHSH inequality an efficiency of η>2sqrt(2)−2≈0.83 is required for a loophole-free violation.[51] Later Philippe H. Eberhard showed that when using a partially entangled state a loophole-free violation is possible for
η>2/3≈0.67,[52] which is the optimal bound for the CHSH inequality. [53] Other Bell inequalities allow for even lower bounds. For example, there exists a four-setting inequality which is violated for η>(5−1)/2≈0.62 [54]
Isn't modern error detection and classical PQ sufficient to work with those odds?
> Historically, only experiments with non-optical systems have been able to reach high enough efficiencies to close this loophole, such as trapped ions, [55] superconducting qubits, [56] and nitrogen-vacancy centers. [57] These experiments were not able to close the locality loophole, which is easy to do with photons. More recently, however, optical setups have managed to reach sufficiently high detection efficiencies by using superconducting photodetectors, [30][31] and hybrid setups have managed to combine the high detection efficiency typical of matter systems with the ease of distributing entanglement at a distance typical of photonic systems. [10]
I wouldn't say that current side-channels, most certainly enabled by hardware, not software, are easier to audit.
Works fine for digital, doesn't work for quantum stuff.
(Polarization of a photon is a two-state quantum system, otherwise known as a qubit.)
That seems... really difficult. I'd always assumed fiber operates by continually absorbing and reemitting photons at low loss. Maybe I've fundamentally misunderstood optics.
Sort of. There will always be attenuation, which is more or less equivalent to losing some fraction of photons. And one can thing of the interaction of light with glass as the photons being absorbed and re-emitted, but thinking about that way doesn’t actually change the result. And, in any case, there isn’t really any such thing as an individual photon: photons are indistinguishable bosons.
In any case, the photons absolutely do interact on the way, but that interaction usually does not affect their polarization, and one of the many counterintuitive effects of quantum mechanics is that, if the polarization is intact, then no one learned it along the way.
Quantum mechanics is bizarre.