List, I have been lurking here for a while. A friend asked me if it was possible to listen in on an analog modem connection and capture the data being sent. Another friend said it could be done. See text below.
I can grasp sniffing packets, but the issues of captureing a modem connection seem to be more complex and involve more steps that I have having troubles being able to position it on a threat level. In fact, it seems that it might be more secure for a number of reasons. Can anyone point me to link detailing how it is done so that I can have a better sense of the concepts involved? Comments? David R. Hibbeln <snip> > ... Is it possible to listen in on an analog modem connection and capture the data from that transmission? Yes, it's possible but it's not trivial like listening to a spoken conversation. Modern high-speed (>2400 baud) full-duplex modems essentially talk to each other continually - as a team - trading information about line quality while negotiating the fastest reliable data rates. The negotiation results in two sets of customized transmit and receive amplitude and phase filter parameters, tuned to the line conditions of the moment in each direction. Unless the third modem is electrically present at the beginning of the connection (difficult if it's a dialup) and is able to use the negotiation exchanges between the end-point modems (difficult while remaining silent), it cannot participate in the negotiation so it will have difficulty producing accurate data in real time, and then only for one side of the connection (each end uses different spectra and common modems have only one receive signal processor). Recorded audio from an analog phone line can also be demodulated into two data streams by post-processing with appropriate equipment. This means that someone can - with sufficient motivation - eavesdrop on an analog data call. If you need a secure link, cipher the data before the modem gets it. <snip>
