

Theoretical breakthrough for quantum cryptography - sev
http://www.technologyreview.com/blog/arxiv/24899/

======
tptacek
This has become my go-to response to QC-related issues. All you need to know
is in the title:

[http://rdist.root.org/2008/10/24/quantum-cryptography-is-
use...](http://rdist.root.org/2008/10/24/quantum-cryptography-is-useless/)

------
orblivion
So, my understanding was that the questions of quantum cryptography stem from
the fact that cryptographic algorithms designed to stump current computers
will be a breeze for quantum computers, so new algorithms will need to be
created to stump quantum computers. I thought that's what was referred to as
"quantum encryption". Is there another name for what I'm thinking of?

But now they're saying that this "quantum encryption" they speak of will be
"perfectly" secure? Does this mean that, once established, cryptography will
no longer need to be a field of study?

Also this: "This solves the problem by embedding it in an extra abstract
dimension, which is independent of space. So as long as both Alice and Bob
know the way in which all these abstract dimensions are related, the third
provides a reference against which measurements of the other two can be made."
blows my mind. The fact that this "other dimension" stuff is no longer just
speculation, but will soon be part of our lives.

~~~
scscsc
It's two different things:

\- one, quantum computers can theoretically do factoring in polynomial time
and therefore theoretically break schemes such as RSA (such schemes are proven
secure _provided_ that some computational problem is intractable -- in the
quantum world the problem becomes tractable)

\- two, you can theoretically use entanglement to achieve "perfect
cryptography". The "perfectness" result is an absolute impossibility result in
physics, and therefore no computer (classic or quantum) can break it. Details
on wikipedia: <http://en.wikipedia.org/wiki/Quantum_cryptography>

The article refers to number two, although in a rather non-technical manner.

Edit: clarifications.

~~~
Daniel_Newby
I would not call it perfect: you still need a classical message authentication
code to protect against a man in the middle attack.

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sp332
"entangled triplets of photons, so-called qutrits"

Actually, a qutrit is just a single tri-state qubit. The term describes
superposition, not entanglement.

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dustingetz
article implies that QC is being used in limited practice right now. i kinda
doubt this. for example, this IARPA solicitation implies that they're doing
baby steps with very small data. of course, if they had it practically
working, it would be classified..
<http://www.iarpa.gov/solicitations_mqco.html>

~~~
sp332
QC is used for key exchange. Private-key ciphers can be more secure than
public-key ciphers, the problem is how to distribute keys securely. You just
need to send about 1k of data (the key), and you only need to send it once.
After that, the two parties use the key to encrypt their messages and send
them using classical channels.

