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The Super-Secure Quantum Cable Hiding In the Holland Tunnel (bloombergquint.com)
Zorro shares a report: Commuters inching through rush-hour traffic in the Holland Tunnel between Lower Manhattan and New Jersey don't know it, but a technology likely to be the future of communication is being tested right outside their car windows. Running through the tunnel is a fiber-optic cable that harnesses the power of quantum mechanics to protect critical banking data from potential spies.
The cable's trick is a technology called quantum key distribution, or QKD. Any half-decent intelligence agency can physically tap normal fiber optics and intercept whatever messages the networks are carrying: They bend the cable with a small clamp, then use a specialized piece of hardware to split the beam of light that carries digital ones and zeros through the line. The people communicating have no way of knowing someone is eavesdropping, because they're still getting their messages without any perceptible delay.
QKD solves this problem by taking advantage of the quantum physics notion that light -- normally thought of as a wave -- can also behave like a particle. At each end of the fiber-optic line, QKD systems, which from the outside look like the generic black-box servers you might find in any data center, use lasers to fire data in weak pulses of light, each just a little bigger than a single photon. If any of the pulses' paths are interrupted and they don't arrive at the endpoint at the expected nanosecond, the sender and receiver know their communication has been compromised.
The cable's trick is a technology called quantum key distribution, or QKD. Any half-decent intelligence agency can physically tap normal fiber optics and intercept whatever messages the networks are carrying: They bend the cable with a small clamp, then use a specialized piece of hardware to split the beam of light that carries digital ones and zeros through the line. The people communicating have no way of knowing someone is eavesdropping, because they're still getting their messages without any perceptible delay.
QKD solves this problem by taking advantage of the quantum physics notion that light -- normally thought of as a wave -- can also behave like a particle. At each end of the fiber-optic line, QKD systems, which from the outside look like the generic black-box servers you might find in any data center, use lasers to fire data in weak pulses of light, each just a little bigger than a single photon. If any of the pulses' paths are interrupted and they don't arrive at the endpoint at the expected nanosecond, the sender and receiver know their communication has been compromised.
The mechanism they describe is also classical physics.
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Change in rx power would trivially detect someone tapping the fiber.
Wouldn't fiber rx power naturally change over time, depending on age of cable, and temperature?
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[QUOTE]"use lasers to fire data in weak pulses of light, each just a little bigger than a single photon."[/QUOTE]
Light comes in units of photons. Saying, "just a little bigger than a single photon," doesn't make sense. Was it two photons? Is this an artifact of averaging and poor journalism, where the target was really 1 photon, and sometimes more are released?
Possibly, but that's not the way a tap would normally be detected. A very short pulse of light would be sent down the cable. Any tap would reflect a tiny bit of the pulse back to the source. With an instrument called a [Optical Time Domain Reflectometer](https://en.wikipedia.org/wiki/Optical_time-domain_reflectometer) the exact location of the tap can be pinpointed.
"Eve of Destruction", it's not just for old hippies anymore...
And don't forget how this "quantum" tunnel actually works in practice.
We didn't get an expected signal at a certain point. Maybe they didn't send it? Maybe they didn't send it because they didn't get ours??
Better call them on the PSTN to ask. Does anyone know who we call? I think it was "Jeff" of "Jim".
No, Jim retired. They don't have a replacement yet. Just call the main office and ask.
Okay hold on. Let me divulge too much to a random person over an insecure line to try to explain what we're even asking about.
She said I need to submit a ticket then their service team will get back to us. We can call and ask them to escalate, but only after we create the ticket.
An hour passes while they create an account in the ticket portal, try to choose something that sort of matches the issue from a crappy set of categories, eventually create a ticket, wait for an email with the ticket number to arrive, etc.
Okay, I called the ticketing desk with the ticket number and they said they'd escalate it.
The next day they get an email from Bob.
Hey guys, this is Bob. We're going to need to reset the entire quantum tunnel. Here are the keys and certs and shit you need to get it done. Email me yours, in regular non-quantum email by 9 AM tomorrow and we should be able to schedule the reset for 10 AM. Feel free to call me on my cell (123) 456-7890 around 10 just so we can both make sure it's working.
The team scrambles to figure out WTF they need to do with the shit Bob sent, and WTF they need to send back to Bob. Eventually, they get it done, and they call Bob at 9:59 AM the next day, but he's working remotely from the inside of a helicopter above an Indian night market. ...ight g..z ... got the stuff th..s ...r se..g that over ...ckly. Let me ...ad and do ...et now. ... ould ha... lights right n.... ... ... ...d you should see... ng now. Let me ..ow when ... ...s ...ng. ...ng, guys? ...t sou... ...ood. I've got s...d green on ... ...d. You should st... ... ...e traffic now. ...ks guys. Le... ...ow if there's any issues.
Uh, yes Bob, we currently have no lights. (That's what he said right? We should have no lights?) They just turned off.
Okay, goo... t me
??? ??? ???
Still
??? Uh, yeah Bob after the lights went out they came back blinking for a bit and they're still blinking. One of them just turned solid green.
??? Yes, we're at solid green too here. (Do we have traffic? How do we know if we have traffic??) Uh, I think we're good now if you see traffic, Bob. Thanks.
The team is now totally quantum secure, for sure! The outage obviously wasn't from someone installing a tap and repeater, and the reset process totally didn't result in the hardware redetecting the link length and recalibrating all timing-related controls. And the team has now printed out a copy of the certs and keys, both Bob's and theirs, and filed them in Joe's desk side cabinet so they could document the procedure in case it happens again. Don't worry, only Joe and two other staff have the key. And the furniture people and custodians. And the keys say "do not duplicate" on them.
No. Quantum entanglement does not violate causality. All particles / information / marketing lies still have to be transported classically, below c.
"If any of the pulses' paths are interrupted and they don't arrive at the endpoint at the expected nanosecond, the sender and receiver know their communication has been compromised" it is just plain damn light path measurement, and has nothing to do with real quantum encryption, and the no cloning theorem.
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You can use classical physics to do quantum stuff.
Quantum Key Distribution uses polarized light, and one interesting property is that unless the polarizes are orthogonal to each other, you're going to have a non-zero probability of light going through. So what you do at the sender end is send pulses of polarized light at random polarizations (say, 0 degrees, 0 degrees, 90 degrees, 45 degrees, 135 degrees, etc). Of course, the pulses are coded to represent your bit pattern, so a pulse could mean a 1, no pulse could mean 0.
At the receiver end, the receiver picks a random polarization and measures the output - either light, or no light. It doesn't matter which.
What happens after sending a copious amount of data is the two ends then compare their polarizer settings and discard the bits where the polarizer setting did not match (e.g., sender used 0 degrees, receiver used 45 degrees). Most of the data will be discarded, but you'll have plenty more where by chance both sender and receiver picked the same polarizer.
You can then do a quick hash to compare the final results - the two hashes should be the same.
Now what happens if someone taps the line? Well, they don't know the polarizer settings, so at best they're going to guess. But the act of inserting the eavesdropping polarizer into the bitstream changes the polarization of the light! If the sender uses 0 degrees, and the eavesdropper uses 45 degrees, light will have a 50% chance of going through the polarizer. But even stranger, at the receiver, if they use a 0 degree polarizer or a 90 degree polarizer, light again will have a 50% chance of getting through. So even though the sender and receiver may both use a 0 degree polarizer, the eavesdropper using a 45 degree polarizer has changed the end result. Maybe the eavesdropper gets lucky, maybe not.
Doing it for a large number of bits and you'll detect the line tap too easily because of it.
If you want to see this in action, you can do the standard two polarizer test, set them orthogonally to each other (so the two polarizers let no light through). Now add a third polarizer AFTER than two polarizers and oddly, you'll get light going through! It doesn't have to be in the middle of the polarizer stack - just the act of the third polarizer interacts with the other two such that some light now goes through where it didn't before makes things extra spooky.
without the decryption keys
That's why this is called Quantum Key Distribution.
Once Alice and Bob* have their keys, the messages are encrypted using standard algorithms and passed over normal fiber optic links.
*Should we change this to Achmed and Boris by now?
Have gnu, will travel.
Who was the chief engineer
This is a key agreement scheme for privacy. Someone wants to keep something secret forever. Today Alice and Bob can use regular encryption to prove they are talking to each other and agree on a secret key using certificates and things like Diffie-Hellman key exchange. We have know how to do this for almost 40 years. The problem with all of this though is that if someone records the Diffie-Hellman key exchange (or other key agreement scheme) and the subsequent communication and computing or math advances in the future to the point where the D-H key exchange can be broken then the communication will no longer be secret. Now if you are the government, communication you do today could be very embarrassing if it was revealed 20 or 30 years from now.
Right now we are back to suitcases with key tables. If an embassy wants to send something that must be kept secret for 50 years, it pretty much has to be physically delivered or the keys for the communication must be physically delivered. Everyone is recording as much communication as they can and trying to build a quantum computer to break the key exchanges. Who will be first? The Americans, the Chinese, the University of Waterloo with money from everyone else???
QKD is simple to understand, I send you a bunch of pulses of photons, you send me back the way you read them, I send you a list of the times you read them the correct way. We now have a subset of photons that we correctly exchanged that we can use as a key. Does it work? As others have pointed out, it only really works if you only send 1 photon at a time. It fails if I send lots of photons each time (which I really need to do) and our attacker has better equipment than we do (which they always will because they get to build theirs after we commit and deploy).