From: tcmay@netcom.com (Timothy C. May)
Date: Tue, 5 Jan 93 09:56:19 PST
To: cypherpunks@toad.com
Subject: Re: purloined letter
In-Reply-To: <Pine.3.03.9301051003.C13150-9100000@ra.cs.umb.edu>
Message-ID: <9301051753.AA25648@netcom.netcom.com>
MIME-Version: 1.0
Content-Type: text/plain


Peter Breton writes:

>  In using encrypted communications, how does one avoid the problem of
> calling attention to the message BECAUSE it is encrypted? "If he went to
> the trouble of coding it, there MUST be something in there!!" Granted that
> if everyone begins encrypting, this problem will vanish... are there
> practical solutions in the meantime? (eg, Codes that look like plaintext?)

The study of how to hide the _existence_ of an encrypted message is
called _steganography_.

Messages have traditionally been:

-placed on microdots and hidden inside letters, under stamps, etc.

-transformed into innocuous-looking messages ("Hello, Peter! Things
are going very well on this January morn.")...typically used with book
codes

-deposited in physical "dead drops," such as in tin cans by the side of
the road, in the branches of trees, etc. (all agreed-upon in advance,
of course)

The cypherspace domain offers new degrees of freedom for hiding such
messages:

-messages may be packed into the "least signficant bits" (LSBs) of
digital images, GIFs and TIFFs, sound samples, etc. As these bits are
at the "noise floor" for modern recording technology, message bits can
be easily made indistinguishable from "real" bits. A simple GIF image,
such as those posted worldwide in the various "pictures" groups, can
easily hold 50K bytes or more just in the LSBs (of each of the
colors). A standard 2-hour digital audio tape (DAT) can carry 80 M
bytes in the LSBs alone! (Imagine the Customs Department trying to
stop someone from carrying out the blueprints to the Aurora spy plane
packed into the LSBs of their favorite tape!)

-similar systems can be used to pack bits into the "ragged right"
margins of messages like this one, where the precise word spacing
carries some bits. Not very many, of course. And the spacing is
susceptable to munging.

-raw data, such as weather reports and sports scores, can be used.
Used since the dawn of espionage, and featured as a plot device in the
French thriller "Soft War," this method is certainly still possible to
use.


As the amount of bits moving around increases dramatically, so, too,
will the avenues for sending encrypted messages.

-Tim May


-- 
..........................................................................
Timothy C. May         | Crypto Anarchy: encryption, digital money,  
tcmay@netcom.com       | anonymous networks, digital pseudonyms, zero
408-688-5409           | knowledge, reputations, information markets, 
W.A.S.T.E.: Aptos, CA  | black markets, collapse of governments.
Higher Power: 2^756839 | PGP Public Key: by arrangement.