loop, the chance of an attacker guessing
right on every transformation can be reduced to a low level.
Hal Finney
ill be somewhat resistant
to such measurements. Eve would not know how to orient her measuring
apparatus and so would likely perturb the photon. The effect would
largely be to introduce noise into the output, which should be detectable
by the participants at some level.
Hal
possible.
In a subsequent message I will analyze how much information Eve obtains
by doing measurements immediately before and after a target cryptographer
has rotated the photon on each circulation.
Hal
en then there is a 1/2 probability that the final measurement
will be right. In all other cases her axes are offset by less than 45
degrees and so there is a better probability than that. So the average
must be greater than 1/2, and in fact with a single measurement there
is a 3/4 chance that the final measurement result will be as it should
have been. This changes the conclusions of my message, so I will post
another version with corrected math.
Hal
obability only slightly further, up to a limit of 1/2.
Therefore the ultimate conclusion from the earlier presentation is
essentially correct, that Eve might as well do as many measurements as she
can in order to get as much information as possible on a single photon,
and that she must accept that her chance of being caught is about 1/2.
Hal
otons without altering
their polarization, but it would present practical difficulties.
> The idea to use quantum physics to get rid of the shared randomness is
> nice. I'm not sure that the approach outlined by Hal can be made to work.
It is still in the early stages of development. I appreciate the many
helpful comments.
Hal
nt.
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.
I'm sure both of these ideas have serious practical difficulties but
perhaps something along these lines could be made to work.
Hal
m so I don't see how one measurement can give you much.
If Eve really can accurately determine the rotation angle by passing
just a single photon through the system that really shoots down the SC
Net idea.
Hal
s would be a "single photon" filter.
So perhaps the idea is not as far-fetched as it sounds.
Hal
lation count, the risk to Eve of gaining any specific amount of
information can therefore be made arbitrarily large.
Hal
consumers to come to understand and believe this as well.
Don't try to use the legal system yourself to force this outcome.
Hal Finney
ge. This is harder for a SC net
because if Eve gets even partial information about who is transmitting,
we can't make her forget it.
I'll keep working on it. Thanks again to John and the others who have
offered helpful criticism and suggestions.
Hal Finney
ether the client
is trusted or not.
Hal
gt; idea doesn't sound too different, but my memory might be wrong. Can anyone
pcw> else offer any insight?
pcw> -Peter
I believe that one of these is a paper by Andrew Odzlyko. Sorry, I
don't have the reference here.
== Hal
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