Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!accuvax.nwu.edu!nucsrl!telecom-request From: John Higdon Newsgroups: comp.dcom.telecom Subject: Re: More on Remote Eavesdropping with an Unmodified Telephone Set Message-ID: <6239@accuvax.nwu.edu> Date: 10 Apr 90 11:54:10 GMT Sender: news@accuvax.nwu.edu Reply-To: John Higdon Organization: TELECOM Digest Lines: 28 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 10, Issue 246, Message 2 of 12 Leichter-Jerry@CS.YALE.EDU@venus.ycc.yale.edu writes: > It's claimed that the reason Ma Bell was so slow to replace the little > incandescent bulbs in multi-line phones with LED's was a security > problem. It seems that voices on the line modulate the power > available to the indicators. The reluctance of the old incandescents > was high enough that no useful information could be gotten from > them, but it was alleged that the LED's provided a nice clear signal > which could be read, say, with a decent telescope and a little > equipment, from the building across the street. Well, I hate to be the thrower of cold water on a great sounding story, but whatever reason Ma Bell had for not modernizing their line indicators wharn't that. The incandescent bulbs were powered from 10 VAC obtained from the KSU power supply. If anything, the bulbs were modulated by other bulbs going on and off within the system. But mainly, they were modulated with 60 Hz from the AC line. Voices on the line had no effect on the bulbs. GTE had key phones with LEDs for years that would plug into standard KSUs. If you tried to "eavedrop" with a photodetector, all you would get would be a big buzz. John Higdon | P. O. Box 7648 | +1 408 723 1395 john@bovine.ati.com | San Jose, CA 95150 | M o o !