r/LessCredibleDefence • u/Ok_Middle8677 • 3d ago

India successfully demonstrates its first free-space quantum-secure communication link for over 5.5 km | India News - The Times of India

https://timesofindia.indiatimes.com/india/india-successfully-demonstrates-its-first-free-space-quantum-secure-communication-link-for-over-5-5-km/amp_articleshow/134677875.cms
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u/barath_s 3d ago edited 3d ago

OP's article says :

. Free-space optics form the foundational bridge for transmitting keys between Earth and orbiting satellites and create the backbone for a global, quantum-secure internet network.

Here's an example of such an experiment ..

https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.94.035001

Only 10 days after the launch, Micius demonstrated QKD between the satellite and a ground station near Beijing, using a protocol known as decoy-state BB84, which uses, instead of entangled photons, weak coherent pulses. In a 273-s connection window, the experiment shared about 300 kilobits of random key—an amount sufficient to exchange an industry-standard 256-bit key every day for 3 years [5]. Using that QKD system, Micius distributed 100 kilobytes of secure keys to ground stations in China and Austria, which were used to secure a 75-minute videoconference between Beijing and Vienna with 128-bit keys, refreshing such keys every second

Also

. With various system improvements, the researchers were able to achieve such a goal, enabling QKD between two ground stations separated by over 1100 km, albeit with only 6 bits of final secure key per pass [7, 8]—enough for a technology demonstration, but not for any practical application

https://physics.aps.org/articles/v15/172

The challenge is the lower ~10km where it transits through the atmosphere

Also note Micius only transmitted at night.

https://ui.adsabs.harvard.edu/abs/2007cleo.conf..956S/abstract

2007 demonstration between the canary islands of la palma and tenerife, 144 km apart.

I might be missing some other nuances, like loss tolerant links etc , daytime links, bit rate and error rate .. so take implications with heaps of salt until someone knowledgeable stops by..

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u/yawkat 3d ago

Free-space optics form the foundational bridge for transmitting keys between Earth and orbiting satellites and create the backbone for a global, quantum-secure internet network. 

While technically true, QKD has limited usefulness in practice. Today's symmetric ciphers and even a classic one-time pad work fine.

People sometimes get confused by the "quantum computing will break cryptography" thing, but that affects specifically some asymmetric ciphers. We have classical replacements for those ciphers. And QKD doesn't even fill the same niche.

It's a solution looking for a problem. 

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u/barath_s 3d ago

https://www.reddit.com/r/QuantumComputing/comments/uvj27p/what_is_the_point_of_qkd/

https://np.reddit.com/r/quantum/comments/14zl18k/usefulness_of_qkd/

https://np.reddit.com/r/cryptography/comments/1poqp7e/whats_so_great_about_quantum_cryptography/

I think the general reaction above mirrors your point.

My takeaway was : QKD is not mature or competitive in practice . But that's not stopping those who seek to develop it. QKD has a theoretical feature that it can be less vulnerable to store and decrypt later attacks. But practically these are not really the current problem and that the elements of cryptography that QKD seeks to strengthen aren't really the weaker elements in a cryptography scheme (?)

Is it right to say that QKD is basically research for hypothetical future knowledge and 'just in case' ?

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u/yawkat 3d ago

QKD has a theoretical feature that it can be less vulnerable to store and decrypt later attacks. But practically these are not really the current problem and that the elements of cryptography that QKD seeks to strengthen aren't really the weaker elements in a cryptography scheme (?)

Right. Store now decrypt later is a concern for asymmetric cryptography. I doubt that will ever become viable for today's symmetric ciphers.

And if you want to be absolutely sure, you can use a one-time pad without QKD. Sure, it's also annoying to use, you need large amounts of key material on both sides of the tunnel and it can't be reused so you can't encrypt terabytes continuously. But it's 100% provably secure, even against quantum computers, and it doesn't require a whole new communication infrastructure.

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u/barath_s 2d ago

ok.

Store now decrypt later is a concern for asymmetric cryptography

RSA, (and ECC) is pretty important and useful. But also I'm not sure how important non-time sensitive cracks there are.

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u/yawkat 2d ago

Sure but you can't replace RSA/ECC with QKD. They do different things.

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u/barath_s 2d ago edited 2d ago

Key distribution for RSA/ECC is relevant to that theoretical feature of QKD, even if it is not practical now

Also, it is plausible quantum cryptography can advance enough to break stored RSA info , which means you may need better key distribution approaches , cryptography schemes etc. (The vulnerability starts from the point of info storage, not the point of break.) It doesn't necessarily mean QKD is the answer, for that risk but who knows if there will be opportunities ? Not a layman like me , anyway.

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u/Revolutionary-Cat981 3d ago

They would do anything but allow starlink ha ?

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u/Jazzlike-Tank-4956 3d ago

Starlink has security concerns

Found the terminals in Manipur, Myanmar border and recently on a ship carrying few tons of cocaine, and they also refuse to allow police further access for investigation

Musk is also a crackpot

Don't think his 30k rupee per month Internet will help remote villages either lol unless he expects government to subsidise it

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u/barath_s 1d ago

Starlink entry into India has nothing to do with QKD or key distribution