Tim mentions that Adobe Photoshop can be used to overlay messages into the low-order bits of a graphics image. Photoshop is expensive, so I'm wondering whether it would be worthwhile for me to write a simple, free utility just for this purpose. I would have it take a GIF file and a binary file to be embedded, and produce an output GIF with the low order bit of each byte changed to be the next bit of the embedded binary file. For output, it would do the opposite - produce a binary file determined solely by the low-order bits of the GIF file. I played with GIF a few years ago and wrote a viewer, so I have some familiarity with that format. It doesn't sound too hard to write a program like this. One concern is whether such a program would be redundant, whether widely available tools already exist to perform the same function. Perhaps there are PD image-processing tools that could be adapted. If anybody knows of any please let me know. For this kind of program to be useful, you'd want to use PGP in its long-discussed "stealth mode". This would be a mode in which PGP would produce output that was basically indistinguishable from random data. Presently PGP puts out some header fields which can be used to recognize that a file is a PGP file. Stealth mode would suppress this information. PGP would not be able to automatically choose which key to use to decrypt such a file, but since most people have only one secret key this would not be a big problem. The PGP developer's group has been talking about this for a long time (over a year) but nobody has cared enough to do anything about it. Maybe it should be done. Hal Finney 74076.1041@compuserve.com