Ok, this isn't exactlty phone phreaking, but it does involve telephones, telephone security, and history. John Young's Cryptome site just posted a formerly classified 1955 FBI/DOD document concerning a pretty interesting thing: a technique for bugging a room using an on-hook telephone by sending ultrasonic frequencies down the telephone line. From the document:
The entire thing was classified TOP SECRET. Apparently more modern telephones, such as the 500-series phone, were not vulnerable to this technique. You can read the full details here.
Speaking of "more modern" phones, makes me think of this.
In 1992 there were a number of cases where the Dutch police just 'happened to have the luck' that the phone was off-hook enabling them to listen in on the room in several cases. Some serious research by BillSF found the method with these high frequency signals down the line. And the simple solution with a small capacitor across the line.
Technical article (in Dutch) about how to build your own circuitry for this: http://www.hacktic.nl/magazine/1824.htm
Posted by: Koos | June 10, 2013 at 06:07 AM