@ Robert Sponge
"... quantum encryption scheme are being cracked ? Is this true ?"
Depends on what you mean by "scheme" and "cracked"?
There have been several attacks against "Quantun Cryptography" that would work against a non "ideal system" (ie a practicle implementation).
However the basic idea is somewhere between "not proven secure" or "not yet broken", depending on your view point.
Issue 1, Is a single photon secure?
Well it's a fundemental idea of quantum mechanics that it is. Which is relied upon in the original QC "ideal system" model.
However sombody came up with an idea to attack it mathmaticaly, so they moved on to using pairs of entangled photons....
Issue 2, Is the secondary channel usage secure?
Alice and Bob use a secondary Shanon channel to tell each other the state of their polariser information.
The QC "ideal system" model assumes that in the secondary channel Alice and Bob can,
A, 100% authenticate each other, and
B, that no information usefull to an evesdropper is communicated.
Both of these realy are nothing more than assumptions as they are very very implementation dependent and to put it bluntly we do not know enough to say (oh look is that a "black swan" trying to fly)....
Issue 3, Is the polariser state selection method secure?
The QC "ideal system" model assumption is that this is 100% non determanistic.
Well in a practical system this gives some very real issues to do with speed and reliability amongst other things.
Now if we assume that due to some problem (ie Eve's intervention or a fault) the method becomes not only determanistic but also predictable to an evesdropper does this give an opening for an active attack?
The answer to this is a very nervous we don't know but we hope not (is that a "black swan" I see flying befor me?)....
Issue 4, Can Alice and Bob reliably detect an attack in the primary channel?
Again in the QC "ideal system" model the assumption is based on Alice and Bobs ability to do statistics...
In practice however there is a problem (is that an elephant in the room?).
Put simply even if there was no tampering with the primary channel the laws of physics dictate that not all of the photons Alice sends will get to Bob.
Therefore at some level an eveadropper will be able to hide in the noise that the statistics will average out
Could such an invisable attacker gain usefull information. It's very implementation specific so again a very nervous "we hope not"...
Issue 5, Can you 100% say only a single photon will be sent by Alice?
In the QC "ideal system" model yes, however in practice it's determanistic, and that means you have three states that Alice might be in for every exchange,
A, No photon sent.
B, A single photon sent.
C, Two or more photons sent.
In a practicle implementation state C is probable for a whole host of reasons....
Issue 6, Is the receiving system for the primary channel secure?
In the QC "ideal system" model yes.
However a real system needs to use photomultipliers and these are problematic to use at the best of times due to the fundemental way they work...
Some real systems are therefore broken due to design / implementation issues around the photomultipliers.
like blinding the photomultipliers with out of band pulses, or other EM fields....
With a little thought you will see that issues 2/3/4/5/6 give an attacker a whole lot of room to play in when not in the QC "ideal system" model. And there are other issues as well...
Which is why there have been attacks against real QC systems, but they usually have had fairly simple solutions to resolve them.
Finaly Issue 1 is the biggie on which the security of the whole idea 100% relies.
Quantum physics is all about mathmatical modeling with probability and theory not about reality (whatever that might be). Dear old Albert amongst others got very upset about it and spoke for God's recreational habbits.
It's also why you occasionaly hear experimental physisists making comments such as "card carrying member of the shut up and calculate club" about their theoretical quantum counterparts.
The rub is this nobody can say honestly that it is secure simply because our quantum model tells us it is not possible to know, we simply belive it is so on faith and one heck of a lot of experimental data ;)
However history shows that our world view changes due to our improved understanding. There is a sort of joke about teaching physics in that you "get taught one lie after another each geting closer to the truth".
Quantum Pyhsics is less than 100 years old and who knows when somebody is going to "take a walk in the park" and come up with another principle that will rock the world of physics as Heisenburg did one cold winters evening. In theory it could happen any time but is it probable ;)