Quantum computing

[Janusz A. Urbanowicz]

On Fri, Apr 20, 2007 at 01:57:46PM +0200, Anders Breindahl wrote:

> Saying that ``there is no such thing'' seems harsh and as if you ignore
> reality. The European Union put its hopes up for implementing a
> ``quantum cryptography'' network of communications. That sort of makes
> the term real in itself.

This is because they are a governement and gov't usually wants to have
super secure comm network for gov't super secret communication.
 
> However, quantum cryptography does have that nice inherent benefit, that
> it _can't_ be eavesdropped, according to said article. That is, after
> authenticity has been established and the line has been paid for:

It can be eavesdropped, but it is impossible to intercept information
that way and the eavesdropping is detectable. Or rather should be:
eavesdropping on QC link is detectable if by rule single photons are
used as transmission units. This is because there's no way to
intercept a photon and reinject it without destroying its quantum
state. However, in commercial installations pulses (batches of
photons) are used, so its perfectly possible to intercept a piece of
the pulse. My quantum-fu is too weak to really know if this makes the
eavesdropping undetectable, but the intuition says that yes.

> I suppose that this is the feature that got the European Union's
> attention.

EU is know for sinking money in very bizarre projects.

> But the attractive part of focusing on the mathematical aspects are that
> -- if provable -- it could give some guarantee ( > reassurance)
> of the unbreakability of the ciphers out there.
> 
> You may not be interested in that, but I am. I too however neither will
> end up a mathematician whose life is focused on solving some single
> problem.
> 
> But I would be interested in the result. I could pick the cipher that
> provably could withstand any battering thinkable over the cipher that
> perhaps couldn't.

But the point is that the ciphers live in the real world and in the
real world it is much easier to do HUMINT (like "ale and whores"
mentioned before, or rubberhose cryptanalysis) instead of trying to
break the mathematically unbreakable. Be it provably unbreakable or
not.

OpenPGP and GPG is about making the idea-based mathematic apparatus
suited to survive in the real world. If you want to see what it takes,
find a movie called "In ascolto" or "The Listening" (it was shot in
Italy by Italians, and was released both in Italian and English), it
is a somewhat loose on technical side, but shows the difference
between mathematical/theoretical and real life security. P2P file
details on (encrypted) request.

Alex
-- 
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