Scientists Race To Establish the First Links of a 'Quantum Internet' 82
ananyo writes "Two teams of researchers — once rivals, now collaborators — are racing to use the powers of subatomic physics to create a super-secure global communication network. The teams — one led by Jian-Wei Pan at the University of Science and Technology of China, the other by his former PhD supervisor Anton Zeilinger of the University of Vienna — have spent the last 7 years beating each other's distance records for long-distance quantum-teleportation. They now plan to create the first intercontinental quantum-secured network, connecting Asia to Europe by satellite."
Re:evesdropping (Score:5, Informative)
Does evesdropping on a quantum message destroy the message?
Not exactly. The eavesdropping is actually detected during the key exchange (the "quantum" part), so if eavesdropping is detected, the message is never sent in the first place. If the key is exchanged without any eavesdropping, the message is encrypted with a one-time pad and sent through more traditional channels.
One-time pads are not vulnerable to cryptoanalysis—not even brute-force searches, as there is a valid key for every possible message (up to the observed message size), and no way to tell which one is the right one. The problem with one-time pads has always been key exchange, since you need a new, never-before-used bit of shared key for every bit of message. Quantum mechanics provides a way to generate shared keys for one-time pads without the risk of anyone eavesdropping (undetectably) on the key exchange.
Re:No US (Score:5, Informative)
Re:Why the satellite? (Score:5, Informative)
Actually, in a practical system, quantum teleportation would generally be used to exchange an entangled photon from which a key can be extracted, the data would sent later using a classical communication technique (like the internet) using classical symmetric encryption scheme (say, like AES-CBC). Of course if the message is small enough, you might just transport the message entangled (instead of just a way to key the encrypted message), but that's much less efficient using current QM entanglement techniques***.
Today key exchange is often done with public-private keys, but the mathematical techniques behind them rely on "trap-door" functions (functions that are relatively easy to compute, but much harder to invert). Hard != impossible, so something that is merely hard to invert today, might be easy in the future. With a quantum key exchange scheme you don't transmit the key, only an entangled photon. Thus can't invert it (with currently known physics), and you can't even intercept it (w/o being detected), so it's impossible to deduce the key even in the future. Of course you could always resort to older time-tested techniques like this [xkcd.com]...
The reason they need the satellite is to transmit the entangled photon (which is used to extract the key). A classical communications channel is effectively a cascade of store-and-forward (every amplifier and digital buffer along the way) so that every stage is making an "observation" and collpasing the quantum state. You basically want to convey the exact same photon you entangled so that the other side can receive it w/o the communication channel observing it in transit. Ideally, you'd bounce a batch of entangled photon off a satellite and the receiver gets the same photons you sent on the other side. Then both sides extract a key from their respective batch of entangled photons and use that key to exchange the message.
Of course, in a fancier system you might use that one entangled photon to quantum teleport some entangled qubits, but that would be more complicated.
***With current QM techniques, you don't really encode a pre-chosen key by somehow "entangling" it into a photon, you are basically creating a type of mind-meld (entanglement) of two photons in a way so that a quantum measurement made on one correlate with the other. With this, magically each side can extract the same information from their respective entangled photons meaning the same bit of information emerges from these measurements. That is why if someone intercepts the photon and retransmit it, both sides would know because they are unlikely have extracted the same bits from the measurments because with currently known physics it's not possible to observe and exactly recreate a quantum state (although apparently you can teleport it). If that doesn't make sense, it's because QM is not supposed to make sense, it just is (or maybe I'm not explaining it very well).
Re:evesdropping (Score:4, Informative)
This is not quite true. True one-time pads are not able to be brute forced, but the pad must be as long as the message (10MB file = 10MB key). This is not how quantum key exchange is expected to work. The quantum key will be measured in KB, to encrypt a secure session or file measured in MB or GB. This means that it is damn secure, but could be brute forced given enough time.
The bit rate on these quantum links is not high enough for it to be practical to exchange pads the size of the file.