At 08:28 AM 3/6/96 +0000, Ed Carp <erc@dal1820.computek.net> wrote:

On Wed, 6 Mar 1996, Nelson Minar wrote:

...

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.

The Quickcam videocameras are $100; they're the next toy to buy after you've got the Soundblaster, CDRom, and 100MB Zip drive. The Macintosh folks will buy them first (:-), but pretty soon they'll be very common, especially for business LAN users to have desktop video. The problem is that, unlike GIFs, CU-SeeMe and other low-bit-rate video compression schemes are _very_ lossy. You can't just put the stego bits in the raw image before running the compression, because they'll get lost, and if you try to fit them in to the compressed image, you've got to do it very carefully or they'll really drastically affect the image. I don't know CU-SeeMe's compression algorithm, but imagine putting bits into a run-length-encoded file: if you put them in the run-length, you'll change the lengths of the runs a lot. If you put them in the color, you'll get lots of streaks of random-looking noise. Either way, it's quite noticeable. So you've got to work very carefully with the algorithm. The other problem with CU-SeeMe is dropped frames, which someone mentioned. That's easier; any email system, especially a stego type, has to deal with lost message. So try to fit your messages into single CUSM frames, and build some tracking or ack messages or maybe message numbering, so you can detect lossage and request retransmits. It can be as complex as X.25-over-stego-over-CU-SeeMe, or as simple as "Message 14 of 32, RSVP". (If you _do_ implement X.25-over-stego-over-CU-SeeMe, you've got a fine April 1 RFC :-) #-- # Thanks; Bill # Bill Stewart, stewarts@ix.netcom.com, +1-415-442-2215 pager 408-787-1281 #