4 ms·

1. Quantum crypto only helps with eavesdropping. To defend against man-in-the-middle attacks you have to use a conventional message authentication code. The sys

1. Quantum crypto only helps with eavesdropping. To defend against man-in-the-middle attacks you have to use a conventional message authentication code. The system is no stronger than the MAC. 2. Quantum nondemolition measurements have been used to detect macroscopic objects with a vanishing probability of interaction. There is a good chance the approach can be adapted to detect photons, breaking quantum crypto. Basically, quantum crypto is at best snake oil and probably worthless.

scythe 13y ago
> Quantum crypto only helps with eavesdropping. To defend against man-in-the-middle attacks you have to use a conventional message authentication code. The system is no stronger than the MAC. False. See e.g. "Quantum protocols for the millionaire problem are trivial", He 2012 http://arxiv.org/pdf/1207.6739 http://arxiv.org/pdf/1207.6739 > Quantum nondemolition measurements have been used to detect macroscopic objects with a vanishing probability of interaction. There is a good chance the approach can be adapted to detect photons. Interaction-free measurement has certainly been demonstrated, but it doesn't do what you think it does. It is provably impossible to measure a state without forcing it to be expressed in the basis of measurement, but this is not the same thing as interaction. I.e. if you measure the position of a particle, you will always find it has a definite position, but you cannot find that it was previously in a state without a definite position. See: http://en.wikipedia.org/wiki/Elitzur-Vaidman_bomb_tester http://en.wikipedia.org/wiki/Elitzur-Vaidman_bomb_tester
- Daniel_Newby 13y ago
  How can #1 be false? No optical measurement can distinguish between good and evil photons. Eve can simply cut the cable, hook a pair of quantum machines up to the ends, and proxy the data between Alice and Bob.
  - anologwintermut 13y ago
    There are information theoretically unbreakable message authentication codes[1] The main point of quantum crypto deployments (at least now) is to protect against future offline attacks (possibly using quantum computer). So in practice, I don't believe these authentication schemes are deployed. [1]https://wiki.cc.gatech.edu/theory/images/9/9e/Lec11.pdf https://wiki.cc.gatech.edu/theory/images/9/9e/Lec11.pdf

scythe 13y ago

> Quantum crypto only helps with eavesdropping. To defend against man-in-the-middle attacks you have to use a conventional message authentication code. The system is no stronger than the MAC. False. See e.g. "Quantum protocols for the millionaire problem are trivial", He 2012 http://arxiv.org/pdf/1207.6739 http://arxiv.org/pdf/1207.6739 > Quantum nondemolition measurements have been used to detect macroscopic objects with a vanishing probability of interaction. There is a good chance the approach can be adapted to detect photons. Interaction-free measurement has certainly been demonstrated, but it doesn't do what you think it does. It is provably impossible to measure a state without forcing it to be expressed in the basis of measurement, but this is not the same thing as interaction. I.e. if you measure the position of a particle, you will always find it has a definite position, but you cannot find that it was previously in a state without a definite position. See: http://en.wikipedia.org/wiki/Elitzur-Vaidman_bomb_tester http://en.wikipedia.org/wiki/Elitzur-Vaidman_bomb_tester

Daniel_Newby 13y ago
How can #1 be false? No optical measurement can distinguish between good and evil photons. Eve can simply cut the cable, hook a pair of quantum machines up to the ends, and proxy the data between Alice and Bob.
- anologwintermut 13y ago
  There are information theoretically unbreakable message authentication codes[1] The main point of quantum crypto deployments (at least now) is to protect against future offline attacks (possibly using quantum computer). So in practice, I don't believe these authentication schemes are deployed. [1]https://wiki.cc.gatech.edu/theory/images/9/9e/Lec11.pdf https://wiki.cc.gatech.edu/theory/images/9/9e/Lec11.pdf