Chaffing & winnowing without overhead

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Jesús Cea Avión (jcea@argo.es)
Mon, 11 May 1998 15:02:59 +0000

You can have chaffing & winnowing without bandwidth overhead, but the
resulting scheme hasn't the original "elegance" anymore. In particular,
you don't send the plaintext on the clear.

The new schema is useful to cypher a document using any standard
signature library, exportable by definition. Very nice :), since you can
use, at last, strong crypto :).

a) When the connection starts, negociate an initial sequence number.
   The sequence number mustn't be reused. We assume a ordered delivery,
   like TCP.

b) Calculate the signature for:

   [sequence]0 -> MAC0
   
   and

   [sequence]1 -> MAC1

c) Compare both MACs and locate the first "different" bit,
   from high to low bit or viceversa.

d) Send that bit from MAC0 if you want to send a "0" or from
   MAC1 if you want to send a "1". 

-- 
Jesus Cea Avion                         _/_/      _/_/_/        _/_/_/
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"My name is Dump, Core Dump"   _/_/_/        _/_/_/      _/_/  _/_/
"El amor es poner tu felicidad en la felicidad de otro" - Leibnitz

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The following archive was created by hippie-mail 7.98617-22 on Fri Aug 21 1998 - 17:17:19 ADT