From: Mikolaj Habryn <dichro@tartarus.uwa.edu.au> Seems to me, if one is talking about videophone type devices, they are transmitting quite a great deal of info, and stegging in a message is quite feasible, is it not? You don't even have to do much of a hardware modification. Do something like having an HF carrier tone in the background, that anyone listening to it can't detect without the knowing what they're listenong for. Or insert a microburst transmission - it'll look like static.

In one of his novels, James P. Hogan had a clever way to insert clandestine messages. There was a moon-earth communications link, and the traffic over the link was monitored to make sure no one was giving away secrets from the installation on the moon to a mole on the earth end. The problem was that they were doing the surveillance on the cleaned-up data stream. The transmission protocol had the semi-standard error correction, whereby blocks of data were transmitted, the checksum was calculated and compared, and bad blocks were thrown away followed by a request for a resend. The spies on the moon merely contrived to send the occassional "bad block" which actually contained the message they wanted to piggyback on the datastream. A listening post monitored the raw data stream and extracted those "bad blocks" which had the right data signature, and the hidden messages were stored and decoded. The people checking the received data which passed the error check never saw the message and assumed all was well, since their own communications gear had already editted it out of the data stream.