[Dailydave] Quantum Key Distribution

Tyler Nighswander tylerni7 at gmail.com
Mon Aug 14 06:08:55 UTC 2017

As a whole QKD between two not terribly far points is not interesting.
People don't really care about just another random free space
point-to-point quantum transmission (even if it's slightly further than the
last one). However, satellite QKD has a few interesting things that are
active areas of research/areas with very practical consequences:
 * very long distance free space transmissions with tolerable
 * QKD with moving objects (like airplanes or satellites) in general
 * quantum networking

To me, quantum networking (establishing a good way to set up QKD between
two arbitrary places) is really the main advantage and cool part of
satellite based QKD. DARPA has been working for around a decade on a small
quantum network, for example, but that requires mostly fiber and some short
line-of-site hops. Scaling that up is not going to be easy; there's been
some research on using existing fiber lines for quantum communication, but
you'd have to replace all the networking equipment with quantum networking
equipment that is entanglement preserving, and that's a huge pain. If
instead you have a satellite network, you now can get relatively easy QKD
between any pair of ground stations without having to worry about updating
vast amounts of infrastructure around the country, and that's the real
advantage: not satellite-earth communications, but earth-(satellite-)earth
key establishment between potentially very distant places.

I don't know enough about the requirements for satellite tracking for QKD
to know if that has practical applications for tracking satellites without
"cooperation", but I would guess it does not. For what it's worth, the
numbers I read in the paper are a satellite of 7.6km/s and a beam width at
the satellite of around 10m. That sounds neat, but not "military satellite
tracking technology" impressive. That sounds like a far less strict
requirement than for GNSS satellites.

As for the original point, if I had to venture a guess as to why there
seems to be growing interest in QKD now: quantum computers are close enough
to being practical that governments want to move their asymmetric secure
comms (no idea how much they use this vs just symmetric crypto). If quantum
computers capable of useful cryptanalytic attacks are 40 years away (that
may be a bit ambitious), and it will take 10 years to implement QKD
networking for government's most sensitive data (that definitely seems
ambitious), that's accepting that data can be decrypted 30 years after it
was transmitted. That's fine for my personal banking information; that's
not fine for lots of sensitive government data. Maybe they received some
intelligence that other groups are simply taking quantum computing
seriously. It would be quite a risky bet to say if the NSA is putting
significant resources towards quantum computing (and they probably are?)
that they won't have practical results for several decades.

So basically: quantum computing is coming slowly, but it's a legitimate
concern; and satellites are interesting because they represent a practical
way to stand up complex quantum networks.

On Sat, Aug 12, 2017 at 5:40 PM, Alfredo Ortega <alfred at groundworkstech.com>

> I don't see it as much as a QKD advancement but as a Satellite and
> tracking advancement, as you have to somehow receive individual photons
> from earth while orbiting at 30 km/s. And if you can track your
> satellites this accurately, you can track everybody elses.
> On 11/08/17 03:41, Jean-Philippe Aumasson wrote:
> > Mostly PR I believe. With this satellite-QKD thing the Chinese probably
> > want to show their own expertise (if they built this alone and not with
> > Western companies), whereas a couple years ago they were discussing with
> > IdQuantique and others to build QKD backbones. Are the Chinese into
> > "quantum supremacy" projects like Europeans?
> >
> > I don't see satellite-QKD as a way to defeat future (?) quantum
> computers,
> > cos satellite-to-earth coms are usually symmetric-crypto based, something
> > unbroken by a QC. BTW QKD research doesn't have much to do with QC.
> >
> > On Thu, Aug 10, 2017 at 5:42 PM dave aitel <dave at immunityinc.com> wrote:
> >
> >> While nothing cryptographic has leaked from the Snowden documents to the
> >> public, Edward Snowden did give up a lot of things to the Chinese to get
> >> out of Hong Kong, and I notice that they've recently invested very
> >> heavily in Quantum Key Distrubtion (for example, shooting satellites up
> >> with entangled photons, etc.)
> >>
> >> So my question is: Is this something they learned about US/Russian
> >> capability against other cryptographics that we are not aware of? Did
> >> they study up and learn something themselves that we are not aware of?
> >> Or is this a total lark or PR stunt? Or maybe it's just not that much
> >> money to them, so they might as well?
> >>
> >> -dave
> >>
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