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That quantum computers can't break symmetric cyphers efficiently is well-known, I just don't see why this makes quantum cryptography obsolete, as it is mostly a

That quantum computers can't break symmetric cyphers efficiently is well-known, I just don't see why this makes quantum cryptography obsolete, as it is mostly about secure key exchange. Also, why are quantum algorithms less secure? There are some possible exploits (e.g. due to problems in the detector), but theoretically the encryption is unbreakable with our current understanding of Physics.

acqq 10y ago
> why are quantum algorithms less secure? It's not about the "algorithms" it's about everything around them. The security is a strong as the weakest link: Again djb, the original article we are supposed to comment here: "Fundamentally, quantum cryptography makes the same mistake as locked-briefcase cryptography: it aims for security in an oversimplified model of the physical world, takes resources away from more serious security techniques, and ends up damaging security in the real world. Quantum cryptography, like locked-briefcase cryptography, also relies on a preexisting secure channel (to authenticate choices of "bases" by Alice and Bob), and does nothing to address the problems handled by public-key cryptography." See also my comment to "quantum credit cards" here as another illustration.
- ThePhysicist 10y ago
  But why does this make research on quantum cryptography worthless? Building a system that delivers the full promise of quantum encryption and addresses the weaknesses of the system is the very goal of such research. Classical encryption schemes would never have gotten to the point they are today without this kind of research funding, so why don't we grant this to quantum cryptography as well? And if the method is so fundamentally flawed as some people want to make us believe, why are several dozen research organizations around the world pursuing it? And why is it a bad thing to talk about applications that seem far-fetched today, like "quantum credit cards"? Blockchain-based currencies were probably also a pretty far-fetched concept 20 years ago, but today they have a fixed place in the currency eco-system.

acqq 10y ago

> why are quantum algorithms less secure? It's not about the "algorithms" it's about everything around them. The security is a strong as the weakest link: Again djb, the original article we are supposed to comment here: "Fundamentally, quantum cryptography makes the same mistake as locked-briefcase cryptography: it aims for security in an oversimplified model of the physical world, takes resources away from more serious security techniques, and ends up damaging security in the real world. Quantum cryptography, like locked-briefcase cryptography, also relies on a preexisting secure channel (to authenticate choices of "bases" by Alice and Bob), and does nothing to address the problems handled by public-key cryptography." See also my comment to "quantum credit cards" here as another illustration.

ThePhysicist 10y ago
But why does this make research on quantum cryptography worthless? Building a system that delivers the full promise of quantum encryption and addresses the weaknesses of the system is the very goal of such research. Classical encryption schemes would never have gotten to the point they are today without this kind of research funding, so why don't we grant this to quantum cryptography as well? And if the method is so fundamentally flawed as some people want to make us believe, why are several dozen research organizations around the world pursuing it? And why is it a bad thing to talk about applications that seem far-fetched today, like "quantum credit cards"? Blockchain-based currencies were probably also a pretty far-fetched concept 20 years ago, but today they have a fixed place in the currency eco-system.