From: "=?iso-8859-1?Q?Jes=FAs?= Cea =?iso-8859-1?Q?Avi=F3n?=" <jcea@argo.es>
Date: Mon, 11 May 1998 06:04:34 -0700 (PDT)
To: cert-es@listserv.rediris.es
Subject: Chaffing & winnowing without overhead
Message-ID: <35571323.D109A0D2@argo.es>
MIME-Version: 1.0
Content-Type: text/plain


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".

-- 
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