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Alexa and Siri Can Hear Hidden Commands

nytimes.com

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Re: Alexa and Siri Can Hear Hidden Commands

#161

Post by tasty_freeze »

Froyoh wrote: post #146
callumprentice wrote: post #122

DolphinAttack: Inaudible Voice commands: https://youtu.be/21HjF4A3WE4

Can't they just limit the activation frequency? Seems easy enough

I don't know anything about it, but based on the name, I'll venture a guess.

The audio system has an A/D converter which samples audio at a specific rate -- say 48 KHz. Aliasing occurs when the input to the D/A convert is above 1/2 the sample rate. A 24001 Hz signal is indistinguishable from a 23999 Hz signal. A 25000 Hz signal is indistinguishible from a 23000 Hz signal, etc.

To eliminate these types of problems, there will be an analog lowpass filter before the sampling circuit. There is a gradual rolloff of signal sensitivity. Aliasing still occurs, but the energy of the aliased signals is significantly reduced.

My guess is you take a voice command, even if it constrained to be say 200 Hz to 2KHz, then invert the spectrum and shift it to the 46-48 KHz range. When this high frequency is played back, due to aliasing, the software after the A/D converter sees it as a 0-2KHz signal, though greatly attenuated. To overcome that, the source audio can be tremendously loud. Humans can't hear it, so it remains stealthy.

Re: Alexa and Siri Can Hear Hidden Commands

#162

Post by denverkarma »

dirkgently wrote: post #159
rootusrootus wrote: post #37

Earlier quoted context omitted.

Sometimes it works great. Sometimes I can't get Siri to do anything right. Anecdotally I've found that Google's voice assistant is quite a lot better. Unfortunately I am unwilling to accept the rest of Google's terms and conditions so I am stuck with Siri for the foreseeable future.

And what are those specific "terms and conditions"? It's funny hoe Google is somehow perceived as evil while Apple or Amazon not. If I have to trust someone with mt data (and we all do), I will choose Google over anyone else.

I disagree that Amazon is not considered evil.

But really I don’t think anyone deeply believes that these companies are good or evil in the personal human sense, rather it’s a question of incentives and interests.

Google makes money by selling me to advertisers. I understand the business value but I’m personally not comfortable with it.

Amazon makes money by selling me other people’s stuff. I’m comfortable with the business, but sometimes I’m concerned that what’s good for Amazon isn’t what’s good for the people who make the stuff I like.

Apple makes money by selling me stuff that they make. This is the business model that I like best, because when they make stuff I don’t like I don’t buy it, and when they make stuff I love I’m happy to give them my money in exchange.

Buying from the maker is the best win-win virtuous cycle, in my opinion.

Re: Alexa and Siri Can Hear Hidden Commands

#163

Post by sailfast »

mkirklions wrote: post #69
sailfast wrote: post #44

I can't recommend highly enough that everyone at least turn on the audible sound when their assistants are listening. At a minimum you should know the kinds of things that end up triggering the device. There's a really wide area of detection and it's interesting to see where that is. I would also recommending changing your default word at a minimum. Then again, I might also recommend ditching the device entirely but…

I want to get rid of my alexa, but my wife uses it as a kitchen timer. We literally dont use it for anything else. Might get one of those philips light sets since our living room is weird... Tbh, id rather not use alexa..

I've started using the device when I lose my FireTV remote. It's a good fallback so the kids don't accidentally start another episode of whatever they're watching and melt down haha.

Re: Alexa and Siri Can Hear Hidden Commands

#164

Post by cozzyd »

tasty_freeze wrote: post #161
Froyoh wrote: post #146

Earlier quoted context omitted.

Can't they just limit the activation frequency? Seems easy enough

I don't know anything about it, but based on the name, I'll venture a guess. The audio system has an A/D converter which samples audio at a specific rate -- say 48 KHz. Aliasing occurs when the input to the D/A convert is above 1/2 the sample rate. A 24001 Hz signal is indistinguishable from a 23999 Hz signal. A 25000 Hz signal is indistinguishible from a 23000 Hz signal, etc. To eliminate these types of problems, th…

That's clever but that's so many dB down with any sane anti-aliasing filter that it would require quite the sound source.

Based on flipping through the pages of the paper (https://arxiv.org/pdf/1708.09537.pdf), it looks like they're taking advantage of the non-linearity in the response at high frequencies to effectively demodulate a lower-frequency signal that was mixed up to ~22 KHz.

Which, if that's what they're doing, is totally awesome!

Re: Alexa and Siri Can Hear Hidden Commands

#165

Post by derefr »

SlowRobotAhead wrote: post #102
adambowles wrote: post #46

Earlier quoted context omitted.

If I recall correctly, the adverts omit a certain frequency range from the assistant's invocation phrase which human's won't notice is missing Edit: Yep, omit / reduce tones in the 3000 - 6000 Hz range https://www.reddit.com/r/amazonecho/comments/5oer2u/i_may_ha...

Which makes WAY more sense than a range outside of human hearing that OP implicated ("inaudible"). Expecting TV's to play tones outside the range people can hear is ridiculous.

Interestingly, though, if psychoacoustic compression was used in when reuploading a video, that 3000-6000Hz range might actually be restored—it’s less information if it’s there than if it’s not.

Similarly, if the video is heard through a phone line, the call might be using a symbolic voice codec, which would also restore the range (in the sense that it’s not even storing sound, just phonemes.)

Re: Alexa and Siri Can Hear Hidden Commands

#166

Post by derefr »

jdietrich wrote: post #142
jimrandomh wrote: post #129

Earlier quoted context omitted.

TV channels already contain inaudible-sound identifiers. Nielsen has people put listeners in their homes, and uses the identifiers to track which channels are getting played.

You can't count on a TV being able to reproduce sounds below about 100Hz or above about 16kHz. The position of the speakers on the back of the TV means you're likely to get a lot of weird phase effects and many TVs have quite heavy audio DSP to compensate for the inadequacy of their speakers. Any hidden signals will need to be in-band and low bit rate with a high level of redundancy.

So, basically, steganography.

Re: Alexa and Siri Can Hear Hidden Commands

#167

Post by tinus_hn »

jdietrich wrote: post #142
jimrandomh wrote: post #129

Earlier quoted context omitted.

TV channels already contain inaudible-sound identifiers. Nielsen has people put listeners in their homes, and uses the identifiers to track which channels are getting played.

You can't count on a TV being able to reproduce sounds below about 100Hz or above about 16kHz. The position of the speakers on the back of the TV means you're likely to get a lot of weird phase effects and many TVs have quite heavy audio DSP to compensate for the inadequacy of their speakers. Any hidden signals will need to be in-band and low bit rate with a high level of redundancy.

You can even less expect all the compression in the system that’s designed to leave out everything people can’t hear, to leave in this signal people can’t hear.

Re: Alexa and Siri Can Hear Hidden Commands

#168

Post by tinus_hn »

dirkgently wrote: post #158
Jun8 wrote: post #6

The interesting thing is that Google Assistant has teh same problem, it's right there in the subtitle. It's interesting that it was omitted from the main title. Rather than journalistic oversight I think this verifies what people have commented many times: that the fact that GA does not have a personalized name makes it to refer to it. SO much so that a very distant third product is included rather than GA.

And ".... hidden commands that are undetectable to the human ear to Apple’s Siri, Amazon’s Alexa and Google’s Assistant." And then "digital assistants like Amazon’s Alexa or Apple’s Siri are set to outnumber people by 2021". Why is Google mentioned in one context but not other?

Dark times are ahead for Assistant. You must warn her of your discovery!

Re: Alexa and Siri Can Hear Hidden Commands

#170

Post by tinus_hn »

TheGuyWhoCodes wrote: post #59

Can't this just be fixed so that Alexa, Siri, etc. will only accept your voice pattern?

While that’s really difficult it would also mean you’d have to train the assistant before you’d be able to use it, which is a big hurdle most customers probably don’t want.
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