Re: Quantum Cryptography can not work

Kristian Gjøsteen wrote:
I would, without sufficient data, guess that much more work has been done
on securing smart card implementations against side channel attacks than
securing QC implementations.

That's my guess, too. I don't even know whether anyone has re-discovered
Adi's attacks; I don't recall seeing them in the papers on QC that
I've read. If side channel attacks on QC had been carefully studied,
then one would assume that Adi's attacks would have been re-discovered.
Then again, the papers I've read on QC probably amount to only a tiny
fraction of the literature in that field, so maybe they have been
re-discovered in some paper I'm not familiar with, for all I know.

Here's one attack I remember from Adi's talk. Assume that the transmitter
apparatus has some kind of polarizing filter that can be put into one of
two orientations to polarize the photon that is going to be transmitted,
following the BB84 protocol. The security of the BB84 protocol relies
on the transmitter to secretly pick an orientation at random and not
tell anyone what orientation was used. The attack is an active attack.
Because moving the polarizing filter requires moving a physical object, it
probably takes some time to move, and stays in any particular orientation
for at least a few milliseconds. The attacker shines a bright light
down the line (in the reverse direction) at the transmitter apparatus.
Some light will enter the transmitter, be reflected internally, come back
out, and on the way out it will be polarized by the polarizing filter.
By looking at the polarization of the reflected light, you can deduce the
orientation of the polarizing filter. You can imagine many variations on
this basic idea. It's a nice illustration of how you may be able to break
a QC system without violating the laws of quantum physics, and how active
attacks on the implementation can render the security theorems irrelevant.
.

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