[52] in cryptography@c2.net mail archive
Re: Multi-drop quantum cryptography article in Nature 385, 47-49 (1997)
daemon@ATHENA.MIT.EDU (Ian Goldberg)
Tue Jan 14 16:44:12 1997
To: cryptography@c2.net
From: iang@cs.berkeley.edu (Ian Goldberg)
Date: 14 Jan 1997 13:28:37 -0800
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In article <199701141916.LAA01920@crypt.hfinney.com>,
Hal Finney <hal@rain.org> wrote:
>This means that Eve can hope to detect a few photons without being
>detected. If she knows the signal/noise ratio of Alice and Bob's equipment,
>she can keep the threshold of extra errors she introduces within the
>reasonable range of existing noise. Depending on how high this is,
>she may be able to acquire a significant number of bits without being
>detected.
I don't think it matters. If I remember my quantum crypto algorithms,
Alice and Bob can place an upper bound on the number of intercepted
bits. They then perform a transformation on the bits they have,
which results in a smaller number of bits, but which has the property
that Eve needs to know a large number of bits in order to get any information
about the result.
For example, if Alice and Bob agree on 3 bits, and they know that Eve knows
at most 1 of them, they can use the 2 bits b1+b2 and b2+b3 to form part
of their key. (I hope I got that right.) Eve ends up with no information
about those two bits.
- Ian
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