A question about quantum cryptography .

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A question about quantum cryptography .

Alright, this is for the QM nerds here.

I don't really know anything about QM but I was watching a conference that Alain Aspect gave the other night and he was saying that quantum cryptography was fundamentally inviolable. As he said "God himself could not intercept a QM cryptographed message" since that if a spy would of intercept the entangled message, this would instantly collapse the wave function thus rendering the information unusable for the both the spy and the real receiver.

The problem I have with this is that I don't see why quantum cryptography would be all that full proof.

If I understood correctly you need 2 channels to send this kind of message. A "quantum" channel, where you send indecipherable entangled photons, and a classic channel where you send a "key" that will allow you to decipher the correlations between the entangled photons.

Let's say that A wants to send a message to B. What would not allow a spy X to hijack both channels thus receiving the EPR photons and the classic key ?

I dunno if my question is clear lol... tell me if it's not.

And please, don't go all Dirac on my ass, I don't know anything about the mathematics behind it : Me = |not that dumb, not that smart>

 

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Girl Dancing In Orbit

Girl Dancing In Orbit wrote:

Alright, this is for the QM nerds here.

I don't really know anything about QM but I was watching a conference that Alain Aspect gave the other night and he was saying that quantum cryptography was fundamentally inviolable. As he said "God himself could not intercept a QM cryptographed message" since that if a spy would of intercept the entangled message, this would instantly collapse the wave function thus rendering the information unusable for the both the spy and the real receiver.

There's a little bit of exaggeration going on there, I think. In basic theory it looks entirely possible to exploit the uncertainty principle to the effect that noone could possibly touch a message sent in quanta without corrupting it, not even the intended reciever. This is all true but nothing is ever as easy as it looks is it? Eye-wink

 

Quote:

The problem I have with this is that I don't see why quantum cryptography would be all that full proof.

If I understood correctly you need 2 channels to send this kind of message. A "quantum" channel, where you send indecipherable entangled photons, and a classic channel where you send a "key" that will allow you to decipher the correlations between the entangled photons.

That's the wrong way round, the key is sent on the quantum channel, public channels are used for the rest of the communication.

 

Quote:

Let's say that A wants to send a message to B. What would not allow a spy X to hijack both channels thus receiving the EPR photons and the classic key ?

Eve can intercept the key signal, but then she must resend the message to Bob using Alice's basis, this means Eve is basically guaranteed to corrupt the message and be detected because when she reads/measures the photons Alice sent she changes them and Alice's basis is presumably completely unknown to her.


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Eloise wrote:

Eloise wrote:

Eve can intercept the key signal, but then she must resend the message to Bob using Alice's basis, this means Eve is basically guaranteed to corrupt the message and be detected because when she reads/measures the photons Alice sent she changes them and Alice's basis is presumably completely unknown to her.

Ok.... This is what I don't get ! (actually there's more than just this... but let's start with this one)

But before, just to be sure that we are talking about the same thing :

Bob is the sender... Eve is (of course) the eavesdropper and Alice (which is my name by the way Smiling ) is the receiver right ?

So...

I still don't see why Eve couldn't hijack every single thing from the start, i.e. the key, the EPR message, Alice's basis and every thing else that I'm not aware of : meaning that Eve is completely disguised as Alice. Even if Bob and Alice noticed that they have been fooled afterwards... Harm's done.

Why can't Eve do that ? Why cna't she disguise herself (from the start) as Alice ?

(sorry again : this is probably a really stupid question but I don't know what I'm talking about and I would like to know !)

 

 

 

 

 

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Quote:  I still don't see

Quote:

 I still don't see why Eve couldn't hijack every single thing from the start, i.e. the key, the EPR message, Alice's basis and every thing else that I'm not aware of : meaning that Eve is completely disguised as Alice. Even if Bob and Alice noticed that they have been fooled afterwards... Harm's done.

Quoting wikipedia "MITM [Man-in-the-middle] attacks are a potential problem in quantum cryptography as well. Recently, hybrid protocols (classical + quantum) have been proposed to deal with it, especially for the three-stage quantum cryptography protocol. [2] [3]"

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Girl Dancing In Orbit

Girl Dancing In Orbit wrote:
Eloise wrote:

Eve can intercept the key signal, but then she must resend the message to Bob using Alice's basis, this means Eve is basically guaranteed to corrupt the message and be detected because when she reads/measures the photons Alice sent she changes them and Alice's basis is presumably completely unknown to her.

Ok.... This is what I don't get ! (actually there's more than just this... but let's start with this one)

But before, just to be sure that we are talking about the same thing :

Bob is the sender... Eve is (of course) the eavesdropper and Alice (which is my name by the way Smiling ) is the receiver right ?

Alice is the sender and Bob the reciever, as in sending 'from A to B' = 'from Alice to Bob'.

Yep, Eve (Eave) is the Eavesdropper for fairly obvious reasons. Sorry for jumping into using those terms, it's difficult to discuss the process without them. 

 

 

Quote:

So...

I still don't see why Eve couldn't hijack every single thing from the start, i.e. the key, the EPR message, Alice's basis and every thing else that I'm not aware of : meaning that Eve is completely disguised as Alice. Even if Bob and Alice noticed that they have been fooled afterwards... Harm's done.

Yeah Eve can create a problem this way. In theory, she can disguise herself as Alice to Bob and Bob to Alice this will get her around detection if she can fool Alice into giving away the details to her as though she were Bob and send something passable to Bob simultaneously.

 

Quote:

Why can't Eve do that ? Why cna't she disguise herself (from the start) as Alice ?

(sorry again : this is probably a really stupid question but I don't know what I'm talking about and I would like to know !)

 

Eve can disguise herself as the reciever (Bob), but to truly get around detection she must also disguise herself as the sender (Alice) and resend or else the real Bob will see big inconsistencies in the transmission, enough to know that the channel is comprimised.

When Alice sends her key to Bob on the quantum channel, they communicate on a classic channel and discuss ambiguous information about what measurements Bob took, he never relates his results across the public channel. Alice then tells him which measurements he took that will work on the key and from the results he got he can deduce her basis and thus the key, the only way to deduce the key from this information is to have Bob's results, which he keeps secret. 

To intercept the transmission Eve has to intercept both channels. She cannot just intercept the quantum channel because she needs Alice to tell her which measurements gave her good results, and she cannot intercept just the classical channel because she would have no results to apply Alice's information to. So she must intercept both channels and talk to Alice as though she were Bob. At the same time, to keep Bob in the dark she has to talk to Bob as though she were Alice, given an ideal set of circumstances Eve could manage this ruse. But this is mainly a problem for the protocol of the tranmission, it remains that Eve can't intercept the quantum channel without destroying the information.

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This is what I thought,

This is what I thought, thanks for confirming it.

 Because this guy, Alain Aspect, seem to be pretty respected, he's the first to have successfully experiment the EPR paradox and has 1000's of honorific titles.

He was really insistent on the fact that "NO ONE" could intercept this kind of message, not even aliens with infinitely more advanced technologies than us...

Since  I don't know shit about QM, I thought I had to be wrong somewhere in my reasoning but I realize that I was not.

Thanks again ! 

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Girl Dancing In Orbit

Girl Dancing In Orbit wrote:

This is what I thought, thanks for confirming it.

Because this guy, Alain Aspect, seem to be pretty respected, he's the first to have successfully experiment the EPR paradox and has 1000's of honorific titles.

He was really insistent on the fact that "NO ONE" could intercept this kind of message, not even aliens with infinitely more advanced technologies than us...

You're welcome. To be fair to Alain Aspect, though, I doubt he was meaning to refer to anything other than the phenomenon of quantum uncertainty, which it would seem is foolproof in it's own right.  

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If he was, it really wasn't

If he was, it really wasn't clear.

He even explained that classic cryptography relied on our assumption that Eve is not more technologically advanced than Alice and Bob as opposed to quantum cryptography that was completely full proof no matter what. 


 

 

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A good layman's book on

A good layman's book on quantum theory is In Search of Schrödinger's Cat: Quantum Physics and Reality. I really enjoyed it.


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Hmm lets drop the bomb I

Hmm lets drop the bomb I have a similar question to QM

1)      If the quantum transmission is destroyed upon reading and NO ONE can intercept this how it  possible to for bob to understand the message without destroying it ?

2)      The old extra nod trick you get the normal and QM  Chantal and start receiving messages QM gets destroyed however this not a problem you just store the transmission you got and resend the same thing to bob in you own QM channel massage generator you are in fact listening  and even a poked calculator can make this.

3)      Simulation is the cay to every thing if you know a transmission gets corrupted upon reading you simulate you own interaction with the QM transmission and calculate it in a similar manner to this little experiment :

 

“M: Every number I will give you has a extra 5 added to it so lets start the transmission 5 , 7 , 9 , 8 OK what number did I just give ?

S1: 5,7,9,8 Master

M: You fail next

S2:0,2,4,3 Master

M: Congratulation You have past ! ”

 

I don’t get how in the world such a QM transmission is prove to this old school trick.

Warning I’m not a native English speaker.

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carx wrote:

carx wrote:

Hmm lets drop the bomb I have a similar question to QM

1) If the quantum transmission is destroyed upon reading and NO ONE can intercept this how it possible to for bob to understand the message without destroying it ?

He can't, once Bob measures the wave collapses into a single state ergo he destroys it too. There is of course, more to the actual transmission of a real message that both parties understand, but basically the answer to your question is anyone who reads the transmission changes the transmission.

 

Quote:

2) The old extra nod trick you get the normal and QM Chantal and start receiving messages QM gets destroyed however this not a problem you just store the transmission you got and resend the same thing to bob in you own QM channel massage generator you are in fact listening and even a poked calculator can make this.

THis most definitely can not be done. A quantum transmission cannot be stored and re-sent in tact. If the message was a pink panther just looking at it could turn it blue or green and there would be no way of knowing that it had been pink. You couldn't store it and not look at it either because your storage device would look at it and that would be the same as though you were looking at it.

 

Quote:

3) Simulation is the cay to every thing if you know a transmission gets corrupted upon reading you simulate you own interaction with the QM transmission and calculate it in a similar manner to this little experiment :

“M: Every number I will give you has a extra 5 added to it so lets start the transmission 5 , 7 , 9 , 8 OK what number did I just give ?

S1: 5,7,9,8 Master

M: You fail next

S2:0,2,4,3 Master

M: Congratulation You have past ! ”

I don’t get how in the world such a QM transmission is prove to this old school trick.

I'm sorry carx, I'm not sure I understand your question, could you rephrase it please Smiling

 

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Girl Dancing In Orbit

Girl Dancing In Orbit wrote:

Alright, this is for the QM nerds here.

I don't really know anything about QM but I was watching a conference that Alain Aspect gave the other night and he was saying that quantum cryptography was fundamentally inviolable. As he said "God himself could not intercept a QM cryptographed message" since that if a spy would of intercept the entangled message, this would instantly collapse the wave function thus rendering the information unusable for the both the spy and the real receiver.

The problem I have with this is that I don't see why quantum cryptography would be all that full proof.

If I understood correctly you need 2 channels to send this kind of message. A "quantum" channel, where you send indecipherable entangled photons, and a classic channel where you send a "key" that will allow you to decipher the correlations between the entangled photons.

Let's say that A wants to send a message to B. What would not allow a spy X to hijack both channels thus receiving the EPR photons and the classic key ?

I dunno if my question is clear lol... tell me if it's not.

And please, don't go all Dirac on my ass, I don't know anything about the mathematics behind it : Me = |not that dumb, not that smart>

 

I dont know about any of this. The fulx capasitor still confounds me. How the hell do you time travel by using a bannana peal as fuel? 

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Brian37 wrote: I dont know

Brian37 wrote:

I dont know about any of this. The fulx capasitor still confounds me. How the hell do you time travel by using a bannana peal as fuel?

Food waste can be used to make biodiesel, though that doesn't explains how Doc Brown got 1.21 Gigwatts from a banana peel Eye-wink that bit was a very large cliam of artistic license. 

 PS The Back to the Future series borrowed the most of its science ideas from Relativity rather than Quantum, so it's a different kettle of fish and a lot of that is dead fish these days anyway.

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Eloise wrote: carx

Eloise wrote:
carx wrote:

2) The old extra nod trick you get the normal and QM Chantal and start receiving messages QM gets destroyed however this not a problem you just store the transmission you got and resend the same thing to bob in you own QM channel massage generator you are in fact listening and even a poked calculator can make this.

THis most definitely can not be done. A quantum transmission cannot be stored and re-sent in tact. If the message was a pink panther just looking at it could turn it blue or green and there would be no way of knowing that it had been pink. You couldn't store it and not look at it either because your storage device would look at it and that would be the same as though you were looking at it.

 

 

Here is the problem , you see if I say store I mean DESTROY the original quantum impulse destroy and its gone OK however the signal has bean detected but the information that it carried got stored on a magnetic disc or other dives. I’m not capturing QM particles and resending the same particles I’m storing the information. OK the next step is to send this stored in magnetic impulses information to the node’s awn  QM particle transmissions generator with generates QM particles identical to the composition of the original transmission and send them going to Bob. You se I still have the original transmission information on a disc and bob got his information too the effect is I have successfully used a listening technique being a little different from  real listening however we get the same result.

I known the transmission and bob gets his massage.

To illustrate this you need to think digital NOT analog , imagine the QM transmission listened and re-created like all of our internet massages passing different control units or nodes.

 

Eloise wrote:

Quote:

3) Simulation is the cay to every thing if you know a transmission gets corrupted upon reading you simulate you own interaction with the QM transmission and calculate it in a similar manner to this little experiment :

“M: Every number I will give you has a extra 5 added to it so lets start the transmission 5 , 7 , 9 , 8 OK what number did I just give ?

S1: 5,7,9,8 Master

M: You fail next

S2:0,2,4,3 Master

M: Congratulation You have past ! ”

I don’t get how in the world such a QM transmission is prove to this old school trick.

I'm sorry carx, I'm not sure I understand your question, could you rephrase it please Smiling

 

 

On the simulation principal I’m sure most non programmers have a difficult time imagining this Laughing out loud. Think of it as a calculation performed to get the error out of your observation. A scientist can illustrate this in a similar faction like light traveling from one point to a another while we know the speed of light and the distance we know for instance that the light reflected from the moon is a little out of date and knowing the distance we can adde the extra speed and get the real position of the moon in real time.  In the moon example we got the human brain performing a simple calculation.

I hope you can imaging this a little better now.

 

Warning I’m not a native English speaker.

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