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From: hes@ncsu.UUCP (Henry Schaffer)
Newsgroups: net.dcom
Subject: Hidden information in datacomm
Message-ID: <3031@ncsu.UUCP>
Date: Wed, 26-Feb-86 21:30:16 EST
Article-I.D.: ncsu.3031
Posted: Wed Feb 26 21:30:16 1986
Date-Received: Sat, 1-Mar-86 00:48:14 EST
Organization: N.C. State University, Raleigh
Lines: 16

<>After reading the discussion on how the inter-character distances
of a printout (easy to do on a laser printer) could be used to encode
information, I started thinking about other places to hide information.
  One place I came up with can hold quite a bit (pun intentional) of
information is the stop bit of serial ascii transmission.  (One can
consider this another example of inter-character distances.)  It
wouldn't take very much special in the way of extra hardware to 
generate a few different lengths of stop bits (e.g., 1, 1 1/4, 1 1/2,
and 1 3/4 bit timings long) and to differentiate between them at 
receipt.  However most data communications equipment will completely
ignore these differences (and have indeed been designed to ignore
them.)
  The information could be lost if the data transmission went through
a regenerator or a packet net, ... .  
  Has anyone been doing this?
--henry schaffer