[Cryptography] Secret key agreement by public discussion from common information

mok-kong shen mok-kong.shen at t-online.de
Tue Mar 8 09:42:56 EST 2016


Am 06.03.2016 um 22:19 schrieb Ben Laurie:
> On 5 March 2016 at 22:43, mok-kong shen <mok-kong.shen at t-online.de> wrote:
>>
>> There is a paper: U. M. Maurer, Secret key agreement by public discussion
>> from common information, IEEE Trans. Inf. Theory, 39(3) 733-742 of 1993,
>> with an IMHO fairly impressive title but having apparently for some unknown
>> reasons been hithertofore ignored in the common textbooks on modern
>> cryptography. The material there is way above my humble knowledge, hence my
>> request: Could some experts kindly give a sketch of the main idea of the
>> paper such that one could get at least a certain rough comprehension of it?
>> Are there good open-source implementations of that key agreement scheme?
>
> The short answer, AIUI, is that you can exploit a noisy broadcast
> system such that the two cooperating parties get an advantage over the
> eavesdropper. In retrospect, this seems obvious (e.g., A tells B
> something, B asks A to repeat certain parts B thinks were badly
> received, A resends them. E gets noisy versions of the original
> transmission, the request for repeats, and the repeats. It seems
> inevitable E ends up knowing a little less than B).
>
> Once you have a disparity of information, you can leverage that up into a key.
>
> The snag is, we have worked hard to eliminate the noise from broadcast. :-)
>
> But its a really interesting idea.

I got elsewhere an idea of a hypothetical attack which I unfortunately
couldn't evaluate with my humble knowlege:

    Eve deliberately injects noise into the system making it seem
    much noiser than it actually is, which Alice and Bob then
    derive their probabilistic models from, but when they start
    exchanging data, Eve removes the noise.

M. K. Shen




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