John Denker writes:
> A much better strategy for Eve is to _not_ make so many
> measurements. Rather, she should preserve the photon in all its analog,
> quantum-mechanical glory and recirculate it back to Bob, bypassing the
> other participants in the ring.
>
> Then Bob, in blissful ignorance
At 10:10 AM 1/20/01 -0800, [EMAIL PROTECTED] wrote:
>This analysis will focus on one particular kind of attack. Eve will make
>measurements of the photon polarization angle as it travels through the
>network and attempt to deduce information about the signals being sent
>by the participants.
Th
This message analyzes the Shining Cryptographers network in terms of
how much information Eve the eavesdropper can hope to get by measuring
the photon state before and after it is rotated. See earlier messages
for more detail about how the SC Net works.
This analysis will focus on one particular
At 09:36 AM 1/18/01 -0800, [EMAIL PROTECTED] wrote:
>Jaap-Henk Hoepman, <[EMAIL PROTECTED]>, writes:
>> In the `traditional' DC Net, how is absence of a message detected?
...
>> If this is a seperately distinguishable outcome of a round, each round may
>> return three outcomes: `0', `1' and `none'
Ray Dillinger wrote, quoting me:
> >Another idea would be for the stations to actually absorb the photon
> >in some manner that preserved its polarization, and then to re-emit it.
> >These could be primed to pass only a single photon.
>
> Now you are talking serious voodoo. I don't think that thi
John Denker wrote:
> At 02:04 PM 1/18/01 -0800, [EMAIL PROTECTED] wrote:
> > I don't think she could learn much with a single photon,
>
> I'm not so sure about that. Remember, photon counters (which measure
> A_dagger A) are not the only measuring devices in the world. There are
> also voltme
At 02:04 PM 1/18/01 -0800, [EMAIL PROTECTED] wrote:
>the rotation stations could
>somehow count or limit the number of photons going through so that they
>would know when there were extra. I think this is possible in theory;
Right, it is. Here's a Gedankenexperiment: temporarily trap the sign
On Thu, 18 Jan 2001 [EMAIL PROTECTED] wrote:
>> Or does somebody have a good defense against this hyper-active attack?
>
>The only thing I can suggest would be if the rotation stations could
>somehow count or limit the number of photons going through so that they
>would know when there were ext
John Denker, <[EMAIL PROTECTED]>, writes:
> Eve need not limit herself to snooping "the signal". What she really wants
> to know is the "state of mind" of the participants, i.e. the settings of
> their rotators. If she knows that, she knows everything. She can, as a
> final step, synthesize
At 11:20 PM 1/17/01 -0800, [EMAIL PROTECTED] wrote in part:
>>The probability that Eve's measurement will leave the result unchanged is
>>3/4, and therefore the probability that she will perturb the result is 1/4.
OK so far. Then, for the case of two measurements,
>>Eve's chances of perturbing
Jaap-Henk Hoepman, <[EMAIL PROTECTED]>, writes:
> In the `traditional' DC Net, how is absence of a message detected?
A practical implementation of a DC Net would require multiple protocol
layers. The lowest layer is the "raw" DC net itself, which has the
property that each person sends a bit str
At 08:35 PM 1/16/01 -0800, [EMAIL PROTECTED] wrote in part:
>In some variants the photon travels around the group multiple times before
>it is measured. Let us call this number of times the "circulation count".
1) Let C denote the circulation count. The idea of having C>1 is very
nice. One
In the `traditional' DC Net, how is absence of a message detected?
If this is a seperately distinguishable outcome of a round, each round may
return three outcomes: `0', `1' and `none'. To represent these quantum
mechanically, you need at least a 3-state quantum system (to make the outcomes
perf
In my earlier posting on the Shining Cryptographers net I stated that
if Eve the eavesdropper made a measurement on a photon in a pure state
in the cryptographer's measurement basis, she would disrupt the final
result with probability 1/2. This is not correct, so I want to give
the right answer h
John Denker writes:
> At 08:35 PM 1/16/01 -0800, [EMAIL PROTECTED] wrote:
>
> >To recap, a group of cryptographers wants to communicate anonymously,
> >without the sender of a message being traced.
>
> To recap in more detail, as I understand it:
>1) The desired result is a plain broadcast mes
At 08:35 PM 1/16/01 -0800, [EMAIL PROTECTED] wrote:
>To recap, a group of cryptographers wants to communicate anonymously,
>without the sender of a message being traced.
To recap in more detail, as I understand it:
1) The desired result is a plain broadcast message, open to the world
(includ
Let me follow up on the Shining Cryptographers idea with a more careful
analysis of the last proposal I made in my earlier posting.
To recap, a group of cryptographers wants to communicate anonymously,
without the sender of a message being traced. They do so by circulating
a photon around a ring
John Denker, <[EMAIL PROTECTED]>, writes:
> At 10:35 PM 1/15/01 -0800, [EMAIL PROTECTED] wrote:
> >Here is a rough idea for a quantum-cryptography variant on the DC Net,
> >the Dining Cryptographers Net invented by David Chaum.
> Hmmm. This seems like a mistake in the physics. If the attacker, E
This will not work.
If the photon starts in the vertical state, and is only rotated either by 0 or
90 degrees, the photon always is either perfectly vertically or horizontally
polarized. Hence the attacker can determine the state of the photon perfectly:
just measure in the standard (non rotated
At 10:35 PM 1/15/01 -0800, [EMAIL PROTECTED] wrote:
>Here is a rough idea for a quantum-cryptography variant on the DC Net,
>the Dining Cryptographers Net invented by David Chaum.
>The photon starts off with vertical polarization. Each cryptographer
>manages a station through which the photo
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