Thomas, > I remember talking to some CIA type folks who said power lines were > being monitored back in the 1960's because electric typewriters > created distinctive voltage spikes marking the stroke of the keyboard > and when the key actually hit the ribbon, and the time delay between > the two spikes determined what letter had been struck...
I hired in at IBM Lexington (Kentucky) in 1977. At that time the site mainly made the IBM Selectric typewriters, but they also continued to make some typebar typewriters. I remember seeing a typebar typewriter that had a big cylindrical housing stuck on one side (a "blivet", to us engineers), and asking "What is that?". I was told that it was a TEMPEST typewriter, and the extra housing contained a flywheel. The engineers had discovered that they could tell what keys were being struck on a regular IBM typebar typewriter by monitoring the AC line somehow. So this TEMPEST typewriter had an electric motor driving the operating shaft through an electric clutch, storing mechanical energy in the flywheel. When you started to hit a key the clutch would disengage, letting the typebar whack the ribbon and paper using the energy stored in the flywheel. Then the clutch would re-engage, to spin the flywheel back up to speed for the next keystroke. Thus someone monitoring the AC power could detect keystrokes, but not identify the keys, which met the TEMPEST requirements. John Barnes KS4GL, PE, NCE, NCT, ESDC Eng, ESDC Tech, PSE, SM IEEE dBi Corporation http://www.dbicorporation.com/ - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
