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> Playing loud music when encrypting/decrypting/typing in your password will defend against acoustic attacks, right? Probably. The answer to Q11 says "The inte

> Playing loud music when encrypting/decrypting/typing in your password will defend against acoustic attacks, right? Probably. The answer to Q11 says "The interesting acoustic signals are mostly above 10KHz". They don't say what the high end of the range is. But I would guess that sufficiently loud music (which usually contains frequencies up to about 22kHz) would mask the sound generated by the CPU.

pbsd 13y ago
From the article: Noisy environment. One may expect that placing the machine in a noisy machine will foil the attack. However, the energy of noise generated in a typical noisy environment (such as outdoors or a noisy room) is typically concentrated at low frequencies, below 10kHz. Since the acoustic leakage is usually present well above this rage, such noises can be easily filtered out during the data acquisition process using a suitable high-pass filter (as we did in our experiments). Also, the signal would be observe during any pauses in ambient noise (e.g., music). Note also that the attacker may, to some extent, spectrally shift the acoustic signal to a convenient notch in the noise profile, by inducing other load on the machine (see below). Thus, a carefully-designed acoustic noise generator would be required for masking the leakage.
- kubiiii 13y ago
  "Thus, a carefully-designed acoustic noise generator would be required for masking the leakage." Like dubstep.
  - sliverstorm 13y ago
    EDM to save the world (by blocking government snooping)! http://www.youtube.com/watch?v=Da4V5vKcGl8 http://www.youtube.com/watch?v=Da4V5vKcGl8
    - kubiiii 13y ago
      They have an electribe ER1 and they modulate so that's gold.
      - sliverstorm 13y ago
        of COURSE we can f@cking modulate this
- kevincennis 13y ago
  I saw that too, but I think they sort of side-step the issue of music. The bit about noise typically being below 10kHz doesn't really apply to most music. If you go run pretty much any modern record through a spectrum analyser, you'll see tons of content above 10kHz. Anyway, I'm certainly not claiming to know with any certainty that loud music would work as a preventative measure against this kind of attack. I just don't think the paper sufficiently proves that it wouldn't be.
  - JonnieCache 13y ago
    This is complicated by the human ear's variation in loudness perception over the frequency spectrum, and the effect this has on music. The stuff over 10k is typically mixed quieter than the stuff under 10k, though it doesn't sound that way. Records with lots of energy above 12-13khz tend to sound pretty awful. https://en.wikipedia.org/wiki/Equal-loudness_contours https://en.wikipedia.org/wiki/Equal-loudness_contours EDIT: also pitch is logarithmic with respect to frequency. 8khz sounds really high pitched.
  - im3w1l 13y ago
    But laptop speakers are notoriously shitty. I don't think laptop speaker output has tons of content above 10kHz.
- cbhl 13y ago
  @kevincennis: A counter-argument to that is that an attacker could run shazam/soundcloud to fingerprint the music, and then subtract the music from the recorded signal. It would be more work, certainly, but I don't think e.g. just playing the radio would be enough to mask the side-channel.
  - kevincennis 13y ago
    That's a really interesting point. I hadn't thought about phase cancellation at all. You certainly couldn't remove everything, since the signal you picked up would be influenced by the speakers/room/microphone/converters/etc, but you still might be able to remove a significant portion of the music that way.
  - jarrett 13y ago
    Filtering out a signal that's in the same band is notoriously difficult. If the signal you're subtracting is known to you, you can simply lock the phases and subtract. That's pretty trivial. But knowing the name of the song doesn't necessarily give you a known signal to subtract. Conceivably, you could be working with a version of the song that was compressed differently than the one playing on the target computer. In which case, the two signals might not have the same waveform, and they wouldn't cancel. To the listener's ear, the signals may sound identical. A good example of this principle is musical instruments. Have a skilled violinist play the same note twice with the same articulation for the same duration under the same conditions. Record each sample the same way. Most listeners would say these two samples are identical. But if you invert one and then mix them, they won't cancel, because they didn't actually have the same waveform. But it's definitely an interesting approach, and potentially viable, if a good filtering algorithm can be worked out. My suspicion is that such an algorithm exists or is at least possible. But I'm not an audio engineer, so I'm not certain.
    - cbhl 13y ago
      I suspect that, in practice, playing music will provide enough of a barrier to mitigate attacks using these side-channels. But then again, in practice, I'd hope that attacks using these side-channels are pretty infrequent to begin with. Besides, in practice, upgrading to GnuPG 1.4.16 (released today) is supposed to also mitigate the key extraction attack using this side channel. The naive approach I suggested would be easily defeated by playing two songs from two different sources; which itself would be defeated by setting up soundcloud on two devices in both places and carefully setting up/analyzing/modelling the room so that you can adjust the signal you're subtracting to account for the distance the sound waves travel and whatnot. I think after a while you just get increasing complexity and diminishing returns -- i.e. it becomes an arms race.

pbsd 13y ago

From the article: Noisy environment. One may expect that placing the machine in a noisy machine will foil the attack. However, the energy of noise generated in a typical noisy environment (such as outdoors or a noisy room) is typically concentrated at low frequencies, below 10kHz. Since the acoustic leakage is usually present well above this rage, such noises can be easily filtered out during the data acquisition process using a suitable high-pass filter (as we did in our experiments). Also, the signal would be observe during any pauses in ambient noise (e.g., music). Note also that the attacker may, to some extent, spectrally shift the acoustic signal to a convenient notch in the noise profile, by inducing other load on the machine (see below). Thus, a carefully-designed acoustic noise generator would be required for masking the leakage.

kubiiii 13y ago
"Thus, a carefully-designed acoustic noise generator would be required for masking the leakage." Like dubstep.
- sliverstorm 13y ago
  EDM to save the world (by blocking government snooping)! http://www.youtube.com/watch?v=Da4V5vKcGl8 http://www.youtube.com/watch?v=Da4V5vKcGl8
  - kubiiii 13y ago
    They have an electribe ER1 and they modulate so that's gold.
    - sliverstorm 13y ago
      of COURSE we can f@cking modulate this
kevincennis 13y ago
I saw that too, but I think they sort of side-step the issue of music. The bit about noise typically being below 10kHz doesn't really apply to most music. If you go run pretty much any modern record through a spectrum analyser, you'll see tons of content above 10kHz. Anyway, I'm certainly not claiming to know with any certainty that loud music would work as a preventative measure against this kind of attack. I just don't think the paper sufficiently proves that it wouldn't be.
- JonnieCache 13y ago
  This is complicated by the human ear's variation in loudness perception over the frequency spectrum, and the effect this has on music. The stuff over 10k is typically mixed quieter than the stuff under 10k, though it doesn't sound that way. Records with lots of energy above 12-13khz tend to sound pretty awful. https://en.wikipedia.org/wiki/Equal-loudness_contours https://en.wikipedia.org/wiki/Equal-loudness_contours EDIT: also pitch is logarithmic with respect to frequency. 8khz sounds really high pitched.
- im3w1l 13y ago
  But laptop speakers are notoriously shitty. I don't think laptop speaker output has tons of content above 10kHz.
cbhl 13y ago
@kevincennis: A counter-argument to that is that an attacker could run shazam/soundcloud to fingerprint the music, and then subtract the music from the recorded signal. It would be more work, certainly, but I don't think e.g. just playing the radio would be enough to mask the side-channel.
- kevincennis 13y ago
  That's a really interesting point. I hadn't thought about phase cancellation at all. You certainly couldn't remove everything, since the signal you picked up would be influenced by the speakers/room/microphone/converters/etc, but you still might be able to remove a significant portion of the music that way.
- jarrett 13y ago
  Filtering out a signal that's in the same band is notoriously difficult. If the signal you're subtracting is known to you, you can simply lock the phases and subtract. That's pretty trivial. But knowing the name of the song doesn't necessarily give you a known signal to subtract. Conceivably, you could be working with a version of the song that was compressed differently than the one playing on the target computer. In which case, the two signals might not have the same waveform, and they wouldn't cancel. To the listener's ear, the signals may sound identical. A good example of this principle is musical instruments. Have a skilled violinist play the same note twice with the same articulation for the same duration under the same conditions. Record each sample the same way. Most listeners would say these two samples are identical. But if you invert one and then mix them, they won't cancel, because they didn't actually have the same waveform. But it's definitely an interesting approach, and potentially viable, if a good filtering algorithm can be worked out. My suspicion is that such an algorithm exists or is at least possible. But I'm not an audio engineer, so I'm not certain.
  - cbhl 13y ago
    I suspect that, in practice, playing music will provide enough of a barrier to mitigate attacks using these side-channels. But then again, in practice, I'd hope that attacks using these side-channels are pretty infrequent to begin with. Besides, in practice, upgrading to GnuPG 1.4.16 (released today) is supposed to also mitigate the key extraction attack using this side channel. The naive approach I suggested would be easily defeated by playing two songs from two different sources; which itself would be defeated by setting up soundcloud on two devices in both places and carefully setting up/analyzing/modelling the room so that you can adjust the signal you're subtracting to account for the distance the sound waves travel and whatnot. I think after a while you just get increasing complexity and diminishing returns -- i.e. it becomes an arms race.