From: Kent Crispin <kent@songbird.com>
Date: Sun, 29 Jun 1997 00:57:52 +0800
To: cypherpunks@Algebra.COM
Subject: Re: Sources for stego images
In-Reply-To: <v03102804afd38b324730@[10.0.2.15]>
Message-ID: <19970628094834.37563@bywater.songbird.com>
MIME-Version: 1.0
Content-Type: text/plain



On Mon, Jun 23, 1997 at 11:38:25PM -0700, Bill Stewart wrote:
> >> >That's the major problem with images, you need to generate your own.
> >> >Unless you fancy writing an image enhancement system, and analyse the
> >> >algorithms in existing systems to ensure that randomness is
> >> >introduced.
> ..
> >Or, set up your own webcam "to watch your coffee pot twice a minute" or
> >something. Merge the crypto stream through the gifs after tweaking the
> >brightness and contrast to avoid 0 and 255 (a light fixture with a pattern
> >of 254/255 values gets suspicious, and is not from thermal noise - a
> >"problem" with monochrome quickcams for night photography).
> 
> Pictures like coffee pots are likely to have parts that change
> (e.g. the state of the coffee pot) and parts that don't change 
> (e.g. the part of the wall that isn't blocked by the pot.)
> This means that it's easy to tell which bits are being messed with,
> if somebody's watching successive pictures.  If the digitization's
> random enough in the low bits, it's a bit better, but a picture of
> something moving helps.  Oceans and fog are great....

Sources of pictures aren't really the problem, though -- it's
developing the widespread habit of people sending references to
pictures along with their email.  For example, if the "cool thing to
do" was to note a link to a favorite photo in your sig (as I have
done, below), then people who were interested in communicating
privately could build up a significant cache of shared pictures.  Code
to automatically compare pictures with the previous version, and
decrypt the embedded messages is no big deal -- the big deal is 
getting people to habitually include links to pictures -- or sound 
files, or whatever...

-- 
Kent Crispin				"No reason to get excited",
kent@songbird.com			the thief he kindly spoke...
PGP fingerprint:   B1 8B 72 ED 55 21 5E 44  61 F4 58 0F 72 10 65 55
http://songbird.com/kent/pgp_key.html
Picture of the day: http://songbird.com/pix/photos/gc8.jpg