art-stego

The recent discussion "Chaff in the Channel" got me thinking about an  
alternative to hiding random bit streams in picture files.  The goal of  
steganography, as I see it, is to provide plausible deniability.  The  
problem with hiding bit streams is that you can never be sure if the  
opponent has developed an analysis technique to prove a particular file  
contains a suspicious bit pattern.

The alternative to hiding bit streams is to not hide them.  Use them to  
generate pretty pictures.  For example, modify a fractal image generator  
to accept a bit stream as input.  Use the bit settings to influence the  
values used to iterate the fractal function.  You don't have to use  
fractals, any function that produces pretty pictures would probably work  
as long as there was a way to extract the bit stream from the final  
picture.  Brute force would probably work fast enough for humans.

One possibility is a screen saver that produces an "infinite" variety of  
pretty pictures by generating a pseudo-random bit stream and using it to  
help generate the next background picture.  Occasionally, the picture  
might be so cool you will want to send it your friends or post it on the  
Net or just keep it around to look at.

The goal is to create an innocent reason for passing around unique images  
that contain random bit streams so we don't have to worry if somebody  
finds the bit stream.  If you live in a country that doesn't outlaw  
abstract art you have plausible deniability.

Jim_Miller@suite.com

The thing that bothers me about existing steganography code I've seen
is that it all uses uncommon communication channels to hide data. For
instance, the "hide data in a picture" programs: useful, up to a
point, but how often do I send pictures to other people? I think to be
effective, methods need to be employed that exploit existing, well
used communication channels.

So here's one idea I've had as a place to hide a channel: network
video, in particular CU-SeeMe video streams. CU-SeeMe is a lowtech
network video application, people running Windows and Macs with a $99
camera and a PPP stack can send about 2fps (160x120) to each other
over the Internet. Times I've used it, bandwidth is about 8kbits/sec
(I'm on a modem).

So here we have a reasonably high bandwidth channel, person to person,
that is already being used a lot on the net. How easy would it be to
borrow a few bits to hide the secret message? Because the image
quality is low (4bpp or 6bpp grey), and definitely nonrandom, you'd
need to be more subtle than just borrowing the low bit.

I think the answer could be found in image processing algorithms.
Spreading a bit out across various pixels would nice, as would some
sort of adaptive algorithm that identifies part of the image that's
safe to hide data in. It's not good enough that the image with hidden
data looks the same to the eye: it has to be statistically identical
to undoctored streams.

The biggest barrier to this I see is that the CU-SeeMe protocol itself
is proprietary, and the only existing free code I know of that does it
doesn't work very well (version 3.0 of a Unix reflector: buggy, now
very old). Of course you have to emulate the normal software 100%
correctly, or the Men in Black will see you're using stego tools.


I should remark that the subliminal channel stuff in digital
signatures is a really beautiful example of steganography.

On Wed, 6 Mar 1996, Nelson Minar wrote:

[Re: data steams to put steno in]
> So here's one idea I've had as a place to hide a channel: network
> video, in particular CU-SeeMe video streams. CU-SeeMe is a lowtech

That's an excellent idea.

The only problem with using CU-SeeMe is that, due to the nature of the 
data being transferred, it is more important to keep up to date than to 
not lose data.  I believe it uses UDP to do this.  There would have to be 
some protection mechanism in the stego patches to tolerate high amounts 
of data loss - the obvious solution would be to loop the data, but that 
is easily detectable, and is not a guarantee that the data arrived 
safely.  Setting up a connection outside of Cu-SeeMe attracts attention, 
especially if there was a correlation between what occurred on that 
connection and what occurred in the LOBs of the Cu-SeeMe connection.


-- Abraham d'Anonymous
   (No relation to Alice)

On Wed, 6 Mar 1996, Anonymous wrote:

> On Wed, 6 Mar 1996, Nelson Minar wrote:
> 
> [Re: data steams to put steno in]
> > So here's one idea I've had as a place to hide a channel: network
> > video, in particular CU-SeeMe video streams. CU-SeeMe is a lowtech
> 
> That's an excellent idea.
> 

[lots of snippage]

Another problem is that in order to get a decent frame-rate CU-SeeMe does 
some image editing of its own: selectively sending only the portions of 
an image that have changed (I.e. the portion of the image that is a 
person who is moving is sent, The bookshelves in the background are not.) 
This could probably be easily gotten around however. 

This seems like a decent idea, however, once the initial obstacles have 
been overcome.. one typical problem with steg is the small number of bits 
that can be hidden.. i beleive a ratio of 1k per 100k is typical. Far too 
small to be useful for most people. Over the course of an hour long 
CU-SeeMe session however you could easily move enough data back and forth 
to provide adequate cover for a reasonablly long bit of cyphertext. 

As long as we're on the subject of stego, has anyone 
discussed/implemented subliminal streams in raw TCP packets? Seems 
possible to do at least on a point to point basis. If you could stash 
your data in the tcp packet itself, it wouldnt matter much what was 
actually being sent across the link. Some possibilities: a telnet client 
with a stegometer that would count the number of hidden bits remaining to 
be sent.. chat clients similarly equiped, etc. Then you could start up 
any client you choose and send data across it until you had gotten enough 
bits to complete transmission of your stego'd file.. just a thought.. ;)



Benji..

On Wed, 6 Mar 1996, Nelson Minar wrote:

> The thing that bothers me about existing steganography code I've seen
> is that it all uses uncommon communication channels to hide data. For
> instance, the "hide data in a picture" programs: useful, up to a
> point, but how often do I send pictures to other people? I think to be
> effective, methods need to be employed that exploit existing, well
> used communication channels.

Then he sez:

> So here's one idea I've had as a place to hide a channel: network
> video, in particular CU-SeeMe video streams. CU-SeeMe is a lowtech

I think it likely that people will be sending GIFs and JPEGs to each 
other far more often than video.  Video is far more an "uncommon 
communications channel" than is a uuencoded picture.
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