Wearable Microphone Jamming
sandlab.cs.uchicago.edu
sandlab.cs.uchicago.edu
> Yikes, please don't do or encourage using these in public - there are many accessibility devices (hearing aids, cochlear implants, etc.) which depend on MEMS microphones to function.
> You could inadvertently make the world much worse for people who already have a difficult time of things. Imagine carting a cellular and WiFi and bluetooth jammer around outside of a Faraday cage - it's insanely irresponsible and inconsiderate.
From the top comment here: https://news.ycombinator.com/item?id=22339548
If the best channel to help the deaf listen clearly is also the best one for letting eavesdroppers listen clearly, then this is a problem best not handled with such a heavy handed solution - possibly not even a technological solution at all.
We already do this by making so many things practically require internet access but then also not making things easily accessible to eg screen readers or text mode browsers
The law has been well-received both by the public and by businesses, with very few actual fines being issued, but many bad pages have been soft-forced into improvement. So it's actually possible, but will probably be much harder in the US, in which business, government and taxpayers/customers seem less aligned.
I also wonder if a simpler approach could be used since the purpose appears to be (can't understand the math) generating noise by driving randomly a number of oscillators around the transducers resonance frequency then induce subharmonic vibrations into the MEMS mics through etherodyne operations between these sounds. If that's how it works, then the DDS chips, the Arduino and the code might be swapped with a less random but likely equally functional set of dissonating oscillators modulated by LFOs (all doable with plain old logic gates); not unlike the old school way of generating cymbals metallic sound in analog drum machines. Here's the Boss DR110 relevant schematic as an example.
it seems to me that this is largely an attack on common preamplifier circuitry. would it be sufficient to ensure that the preamps implement low pass filtering? or is the issue more in the microphone element?
"For the above idea to work with unmodified off-the-shelf microphones, two assumptions need validation. (1) The diaphragm of the microphone should exhibit some sensitivity at the high-end frequencies (> 30kHz). If the diaphragm does not vibrate at such frequencies, there is no opportunity for non-linear mixing of signals."
The devices tested include hearing aids, smartphones, smart watches, etc, which are all likely to include small surface mount MEMS microphones. I doubt any of these techniques will work against a larger dynamic or condenser microphone, where the mass of the diaphragm makes the system inherently insensitive to ultrasonic frequencies. There's a reason the jamming signal is inaudible, and it's not because our auditory cortex contains an ideal lowpass filter.
"When these tones arrive together at the microphone’s power amplifier, they are amplified as expected, but also multiplied due to fundamental non-linearities in the system"
"In practice, however, acoustic amplifiers maintain strong linearity only in the audible frequency range; outside this range, the response exhibits non-linearity."
That suggests to me that the nonlinear mixing isn't occurring in the MEMS structure, but rather the amplification stage. Perhaps the authors' language is imprecise?
They do say immediately after the last bit:
"The diaphragm also exhibits similar behavior [non-linearity]."
Is just the diaphragm's nonlinearity sufficient for the effect?
All I can contribute is that nonlinearity in audio systems is also known as distortion, and it's impossible to eliminate entirely because every system, whether electrical mechanical or even digital, goes nonlinear when it reaches its amplitude limits. Some more gracefully than others.
Seems like it would be difficult to tease out the relative contribution of the MEMS element and the preamplifier because the preamps are typically implemented on ASICs in the same package. So that might be speculation on the authors' part.
Still, this may be the only real option in public spaces (i.e. outdoors). If you're okay with people knowing that you're trying to avoid being recorded, then this would probably be fine.
Smart assistants are usually not recording really high quality audio, it takes more time to process it and more time to send it back home so they are going to a lower sample rate than typical voice recorder app would use. Siri uses a 16KHz sample rate (Fs=16KHz) which is enough to put the whole human vocal range in the 1st Nyquist zone (less than Fs/2). Playing a sound at 26KHz (3rd Nyquist zone, >Fs but <1.5*Fs) is going to cause a reflection across Fs. So the 26KHz tone, sampled at 16KHz, creates a tone at 10KHz which could be enough to confuse a naive implementation of a smart assistant. Ideally, you want fix this by either installing an analog filter so the ultrasonic noise can never reach the ADC or sample the whole range (up to 44.1KHz is a good start) and filter digitally.
There is a paper called DolphinAttack [1] where they attempted to use the ultrasonic audio band as an inaudible attack vector. You could play an ultrasonic noise that no one can hear except for the smart assistant.
[1] https://gangw.cs.illinois.edu/class/cs598/papers/ccs17-hidde...
It is illegal public and most commercial spaces as most organizations need to follow anti-discriminatory legislation. Spaces unusable by people with hearing aids, hearing dogs or just very good hearing is not going to happen.
(On standalone device limitations)
>(2) They rely on multiple transducers that enlarge their jamming coverage but introduce blind spots locations were the signals from two or more transducers cancel each other out. If a microphone is placed in any of these locations it will not be jammed, rendering the whole jammer obsolete.
>To tackle these shortcomings, we engineered a wearable jammer that is worn as a bracelet, which is depicted in Figure 1. By turning an ultrasonic jammer into a bracelet, our device leverages natural hand gestures that occur while speaking, gesturing or moving around to blur out the aforementioned blind spots.
Edit: sorry, I went against my better judgement and decided to respond sarcastically to the other comment. I was being facetious.
It would be interesting to evaluate this device’s impact on telephonic conversation!
I hope there is a switch to turn the device on/off. Otherwise you won’t be able to talk on the phone :-)
"During a phone interview, Mr. Lopes turned on the bracelet, resulting in static-like white noise for the listener on the other end."
https://www.nytimes.com/2020/02/14/technology/alexa-jamming-...
Rodents less likely to nest near you may be a positive thing.
he said, "Watch the moths." It turns out the moths, through evolution, had developed their own electronic countermeasures to jam the bat radar
https://steveblank.com/2009/03/23/if-i-told-you-i%E2%80%99d-...
Seems like countering it might be a use-case only important to specialty buyers who want to get around this kind of protection. Even if it wasn't that difficult to counter, there might not be enough incentive for most off-the-shelf mics and specifically Alexa/phone/etc to do so.
Interesting, what are related theories I can learn about it deeply?
> always listening, recording, and possibly saving sensitive personal information
without any evidence to support it. I get that they're just setting up context for their device, but they're also making some pretty serious (and widely disproven) accusations.
They left 4 related articles in the publication please read the actual paper before criticizing it.
> and widely disproven
I personally never heard of it. Any evidence?
While I do appreciate that the cited sources in their paper, I would have appreciated actual information security papers rather than mainstream media articles.