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Saturday, October 6, 2012

Audio Feedback Bug, Physical Security Systems, and Oscilloscope Research

Every once in a while I use an audio double adapter for recording or playback purposes. Recently, I noticed a bizarre bug though. If you understand how playback control circuitry works on headphones you'll understand that an electrical signal is sent to the device which (depending on the signal) will cause it to play, pause, rewind, and so on. With this particular adapter though under certain conditions signals would be looped over and over again. The only way to break it was to disconnect it from the second connected device or disconnect the adapter completely. I've thought of creating software to filter the signal itself but it doesn't seem to be much of a problem at this stage.

If you've been reading this blog of late you'll have realised that I've been conducting research into security of late. My latest work has involved looking at physical security systems. One of the things I've been looking at is how easy it is to disable low to mid level priced security devices (We'll neglect basic techniques such as physical destruction, cutting the power, and disconnecting the speaker siren.). What I've discovered is that what you see in the movies is basically what you get in the real world as well. If circuitry is reasonably simple it's almost trivial to see which particular pins need to be shorted in order to disable the system. On multi-PCB systems though things may be slightly more complex but the theory/practice remains the same. If you focus in on the switching circuitry/section (It doesn't matter whether the system depends on a keypad, cards, or something else. The principles are the same. You can choose to hack the keypad, cards, etc... but this is by far the easier option if it's available. Learn to use a continuity tester or multimeter. It will serve you in many more ways than you'll ever expect. Use alligator clips. They'll save you a lot of time.) then you can disable it fairly quickly.

Just like computer security though you'll notice that there are a lot more ways to disable it rather than enable it. If you don't want to go deaf with the siren disconnect it and reconnect it to a standard, adjustable, powered speaker.

The obvious countermeasures are to use alarm systems that depend on a 'heartbeat' or which are (or can be) monitored remotely, use something where circuitry between the reader and the authenticator are separate, or watch for PCB's which simply are complex to trace/read which gives the attacker less time to examine it. Other possible measures are actually painting over your PCB (to stop examination), ensuring that your alarm system is as physically secure as possible (It's ironic how many keypads/security systems often have openly available screws/ports through which to access the PCB easily. If you're confident in the reliability of your system glue it together or use tamper proof stickers.), and a good guard dog.


If you don't have an oscilloscope (cheapest handheld one I've seen is available for about 300 locally though they are often available inexpensively second hand) then there are other options. Some options include using sound cards and data acquisition cards (you need to ensure that the voltages are 'safe' for your card and your cards are fast enough to capture the data from the system being examined though) in combination with relevant software to examine the resulting waveforms.


Amazing how far translation technology has come. On the fly, verbal translation is now possible.


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