
The quantum internet has arrived (and it hasn’t) - cpheinrich
https://www.nature.com/articles/d41586-018-01835-3
======
tristanj
Do we really need a quantum internet though? Our current non-quantum
encryption system honestly works very well. Symmetric encryption is
statistically unbreakable at large enough key sizes. Using a brute-force
attack on a 256-bit AES key, it would take billions of years to crack, even
with a quantum computer. Given a large enough key size (1024-bits), it would
take longer than the heat death of the universe to crack such a key.

For key exchange, quantum encryption is definitely better, but how much better
is it than switching to a quantum resistant key exchange algorithm? And
switching to quantum encryption would require a complete internet
infrastructure overhaul, meaning fiber optics everywhere, all new routers
(would packet routing still work?), new cell towers, and no more copper lines
for internet.

Is this complete architectural overhaul worth it, just to decrease the chance
of being hacked from 1/2^256, to 0? To me the benefits seem marginal.

It reminds me of flying cars: yes it's the future, yes they work, yes we can
do it, but is it practical?

~~~
abdullahkhalids
There are a few hopeful candidates for quantum-secure classical asymmetric key
systems, but there are no strong proofs that they are secure against either
classical or quantum systems. Without these proofs, and danger that any day
someone can come up with a way to break any and all such classical encryption
systems, its valuable to at least develop quantum key distribution systems.

In other words, the chances of being hacked are far greater than 1/2^256. They
depend on how much secret progress you think organizations such as NSA have
made in mathematics. They depend on how likely you think someone will actually
develop a quantum resistant asymmetric encryption scheme before large scale
quantum computers are built. Of course, there is also a non-zero chance of the
quantum internet being hacked.

Yes, developing a quantum communication system will require massive
infrastructure. However, its possible to use quantum communication links for
regular classical communication i.e.\ once the quantum communication link is
high bandwidth enough, you can just route all your classical communication
through it. So, its not the worst possible thing to have these links up.

~~~
hannob
> There are a few hopeful candidates for quantum-secure classical asymmetric
> key systems, but there are no strong proofs that they are secure against
> either classical or quantum systems.

While technically correct, this is totally misleading. There are no
cryptosystems at all that have strong proofs of security. (Minus one time
pads, which are completely impractical.) Your QKD system also depends on a
bunch of assumptions that you can't prove.

------
walrus01
One of the huge problems of requiring lossless photon transmission through
fiber: This will break all currently known approaches to DWDM. It is not
economical for inter-city transport between ISPs to require its own dark
strand pair, no WDM of any type, in most scenarios. There's a reason why
people want to be able to do things like 100/200/400GbE coherent frequencies
in a 80-channel DWDM bandplan.

------
tomonl
Stephanie Wehner also taught a great course on quantum cryptography.

[https://ocw.tudelft.nl/courses/quantum-
cryptography/](https://ocw.tudelft.nl/courses/quantum-cryptography/)

~~~
marius_k
She can explain the topic really well. I attended her talk at SHA2017[0].

[0]
[https://media.ccc.de/v/SHA2017-361-invitation_to_help_build_...](https://media.ccc.de/v/SHA2017-361-invitation_to_help_build_quantum_internet)

------
JepZ
That woman on the title picture somehow reminded me of Stargate's fictional
character Jeanie Miller :D

[https://78.media.tumblr.com/tumblr_lifvvogP0H1qh5nggo1_500.j...](https://78.media.tumblr.com/tumblr_lifvvogP0H1qh5nggo1_500.jpg)

------
7ero
I'm a bit confused by the process of entangling photons emitted by two
distinct qubits, wouldn't entangling those photons affect the state of the two
original distinct qubits? Or is that simply how entanglement works?

~~~
krastanov
Very naively, the following happens: Qubit A is entangled with Photon A. Qubit
B is entangled with Photon B. Photon A and Photon B are measured __together
__in way that does not permit distinguishing the two photons (this is where
the magic happens) and destroyed. This results in Qubit A and Qubit B now
being entangled.

~~~
kenning
Thanks, this helps a lot

------
hartator
> quantum particles [...] has been used for years to enhance data encryption.

As an entropy source or more?

~~~
krastanov
No, it is way more interesting than that. With entangled particles together
with a public unencrypted classical communication channel you can create a
protocol to exchange information securely. That protocol does not rely on any
computational complexity assumptions, rather only on the assumption that the
laws of quantum mechanics are correct. There are some caveats, but it is still
an amazing construction.

[https://en.wikipedia.org/wiki/Quantum_key_distribution](https://en.wikipedia.org/wiki/Quantum_key_distribution)

[https://en.wikipedia.org/wiki/BB84](https://en.wikipedia.org/wiki/BB84)

------
EGreg
Can this enable FTL communication?

[https://www.livescience.com/59810-quantum-teleportation-
reco...](https://www.livescience.com/59810-quantum-teleportation-record-
shattered.html)

~~~
tomonl
No, a classical connection (e.g. the internet) is needed for quantum
teleportation. This classical connection won't be faster than light.

------
SCAQTony
A cat walks into a bar... or did he?

------
mratzloff
No, it hasn't.

Also, re: this image[0], I thought entanglement couldn't be used to send
information? Isn't this complete nonsense?

[0] [https://media.nature.com/w800/magazine-
assets/d41586-018-018...](https://media.nature.com/w800/magazine-
assets/d41586-018-01835-3/d41586-018-01835-3_15461638.jpg)

~~~
tomonl
The image is correct. The information is sent over a classical channel, not
using entanglement.

~~~
krastanov
While the image is correct, your statement would be a bit misleading to
novices:

You can not transfer the state of the qubit over a classical channel. You need
both a classical channel __and __entanglement. Or in other words: a bit can be
send over a classical communication channel (by copying it), but to transmit a
qubit (which can not be copied due to its quantum nature), you either need to
carry the physical qubit over, or use entanglement __together __with classical
communication.

~~~
IntronExon
The essence of the issue for many, who seem to equate entanglement with FTL is
that a classical channel is _required_. Without that, you’re just sending
noise over your quantum channel.

Plus we get to keep cause and effect ordered, as a little bonus.

------
crenellated
Ugh. Images like this are why no one should ever pay attention to fluff
magazine articles about quantum anything:

[https://media.nature.com/w800/magazine-
assets/d41586-018-018...](https://media.nature.com/w800/magazine-
assets/d41586-018-01835-3/d41586-018-01835-3_15461638.jpg)

The person who created that picture had no clue what the diagram is supposed
to represent. They obviously created the infographic based on a conversation
with someone who probably also doesn’t completely understand what their
talking about.

Why articles like this must be written at all is what gets me. Someone out
there wants this topic to have an article published, and they just don’t
really care if the information it presents lacks accuracy.

~~~
krastanov
I work in the field, on my way to a doctorate, and I do not see anything
bothersome with the infographic. It is well made and factual.

