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Path: utzoo!mnetor!uunet!seismo!ll-xn!ames!xanth!kent
From: kent@xanth.UUCP (Kent Paul Dolan)
Newsgroups: sci.math,sci.crypt
Subject: Re: Encryption of Hoffman coded text
Message-ID: <2173@xanth.UUCP>
Date: Wed, 31-Dec-69 18:59:59 EDT
Article-I.D.: xanth.2173
Posted: Wed Dec 31 18:59:59 1969
Date-Received: Fri, 21-Aug-87 06:41:34 EDT
References: <10489@linus.UUCP] <7876@mimsy.UUCP> <10604@linus.UUCP> <1227@hropus.UUCP> <1034@faline.bellcore.com> <851@klipper.cs.vu.nl> <292@markle.randvax.UUCP>
Reply-To: kent@xanth.UUCP (Kent Paul Dolan)
Organization: Old Dominion University, Norfolk Va.
Lines: 33
Keywords: compressed bit boundaries <> uncompressed character boundaries
Summary: What about adaptive arithmetic encoding?  Worse to decrypt?
Xref: mnetor sci.math:1920 sci.crypt:526


I am currently involved (for a communications package) in a FORTRAN
implementation of the recently published (CACM V30N6 June 1987
p520-540) adaptive arithmetic data compression algorithm.  (It works
fine; I needed to talk across a line that would only accept printable
ASCII characters, so I adapted the algorithm to encode to 13 bits and
then pass 6.5 bits per message byte. (95*95 printable ASCII characters
holds 13 bits of information quite conveniently.))  This seems to be
even more interesting than the adaptive Huffman encoding, for purposes
of confusing decrypters, because individual bit boundaries don't match
with individual character boundaries, NOR VICE VERSA!  A particular,
non-standard start-up encounter count list for the characters (in the
adaptive form, which is the only interesting one) might be a
sufficient encryption scheme by itself to "lend confusion to the
enemy".  In any case, I'm pretty sure that every bit in the compressed
message depends at least slightly on every character up to then in the
uncompressed message.  I don't have the math skills to analyze this,
but I'd sure like to see comments on this one from the net!

Kent, the man from xanth.
--
Kent Paul Dolan, LCDR, NOAA, Retired; ODU MSCS grad student	 // Yet
UUCP  :  kent@xanth.UUCP   or    ...{sun,harvard}!xanth!kent	// Another
CSNET :  kent@odu.csnet    ARPA  :  kent@xanth.cs.odu.edu   \\ // Happy
USPost:  P.O. Box 1559, Norfolk, Virginia 23501-1559	     \// Amigan!
Voice :  (804) 587-7760    -=][> Last one to Ceres is a rotten egg! -=][>

I code reactor power plant control in C.
I add "count_of_recent_alarms" to "count_of_rods_to_lift".
C has weak type checking; the compiler doesn't notice.
A major coolant valve sticks, a spate of alarms occur.
All die.
Oh, the embarrassment!