Re: Some questions about BB84
- From: "tadchem" <tadchem@xxxxxxxxxxx>
- Date: 14 Apr 2006 02:39:15 -0700
ergun wrote:
Hi,
I have been reading Quantum Cryptography related papers for a short
while and I encountered some questions. Could any one of you clarify
them for me ?
1) Why the last bit of each block is discarded in reconciliation
process (parity check) of BB84 algorithm?
This is 'sci.physics' - your BB84 allgorithm is alien to us. Try a
computer cryptography group.
2) It is said that Eve can not eavesdrop without being detected because
she can use only rectilinear filter or diagonal filter. If she chooses
the wrong one this would change the polarization of photon and she can
be detected. I don't have any idea about filters but is not it possible
to make ONE filter that is both diagonal and rectilinear so that any
kind of photon polarization can be read without changing it ?
No. A polarizing filter sorts photons according to the alignment of
the filter. Photons polarized perfectly in line with the filter pass,
while those polarized perpendicular to the filter are blocked.
Photons that are not either with or against the filter have their
polarizations changed so that they are either with the filter (and
pass) or against the filter (and are blocked) randomly according to
angle of their alignment versus the alignment of the filter.
3) It is said that in privacy amplification step, n-m-s blocks are
chosen and their parity bits form the key for encryption. What does the
values of m and s depend on?
Again, this is not physics. This is cryptographic theory and is better
discussed elsewhere.
Tom Davidson
Richmond, VA
.
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