From: plaz@netcom.com (Plaz)
Date: Mon, 28 Feb 94 16:00:54 PST
To: cypherpunks@toad.com
Subject: standard for stegonography?
Message-ID: <199403010001.QAA18620@mail.netcom.com>
MIME-Version: 1.0
Content-Type: text/plain


<Sorry this post was supposed to go to the whole list yesterday. I forgot
to redirect to cypherpunks, oh well.>

Derek Lynn Upham replies to Jef Poskanzer:
>> Is there a standard for stego yet?  I just added stego and de-stego
>> filters to my pbmplus image toolkit, using a simple protocol I made
>> up on the spot.  Now I'm wondering if I should make them compatible
>> with existing stego tools.
>
>There appear to be two existing steganography packages for images.
>One is "jsteg", a Unix-based system which stores data in JFIF-
>compliant JPEG images; it is based on version 4 of the cjpeg/djpeg
>package.  The other is "Stego", a Mac-based system which stores data
>in Mac PICT files (I think---I don't have a Mac to examine it).
>
>"jsteg" is available in the Cypherpunks FTP archive in the
>applications subdirectory as the original jpegsrc package, plus the
>patches, plus a README file.  However, you might be better off
>tracking down the "Stego" sources since "jsteg" stores its data in a
>rather odd way (see the docs for more information).
>
>Derek

jsteg's stores it's data based on the compression algorithm and is tied
tothe format (jpeg, which is a lossy compression format).

Stego (which I contributed to and consulted on) actually has a relatively
format independant way of storing the data in the picture. Stego was
written by Romana Machado (romana@apple.com) Check out the article in the
latest WIRED (p. 26?) and the soon to be released (any day now) bOING
bOING.

Quoted from the stego readme:

>Stego rasterizes the image, then stegs data into the least
>significant bit (or LSB) of each of the RGB color values. (In the
>case of indexed color, Stego stegs data into the LSB of the index
>values.) The file length of the data file to be stegged is hidden
>in the LSB's of the first 32 steggable bytes. To disguise this
>value somewhat, I take the second to least significant bits of the
>second 32 steggable bytes and XOR these with the 32 bit file
>length, and then steg the XOR'd file length into the LSB's of the
>first 32 steggable bytes.

Source isn't really necc., but if you feel you MUST have it: contact
romana@apple.com.