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Headphones can be hijacked to surreptitiously record audio

wired.com

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Re: Headphones can be hijacked to surreptitiously record audio

#121

Post by qb45 »

21 wrote: post #84
chinathrow wrote: post #80

Earlier quoted context omitted.

Reads like a back door to me.

This feature allows you to plug any audio device (input or output) into any audio jack on the computer and it will JustWorkTM. Even if the jacks are color coded or annotated, these day they are actually universal. So it's more of an accidental backdoor.

They aren't fully identical, though. On my motherboard with some Realtek 8xx chip, plugging headphones into front panel jack, green jack, black jack and everything else produces progressively worse quality. Mainly bass suffers and only when driving headphones (no problem driving amps) so either these outputs have lower power capacity on the chip or DC blocking capacitors on the motherboard are smaller.

Re: Headphones can be hijacked to surreptitiously record audio

#123

Post by detaro »

mikey_p wrote: post #122
mark-r wrote: post #11

Analog headphone amplifiers are quite easy to come by and can fix the problem for the ultimate paranoids.

This exploit only works with analog headphones. They don't solve anything.

You won't get any signal back through an amplifier between the ouput (now input) and the headphones, so yes, adding one helps.

Re: Headphones can be hijacked to surreptitiously record audio

#124

Post by kuschku »

Declanomous wrote: post #61
kuschku wrote: post #50

Earlier quoted context omitted.

> with a pair of Sennheiser headphones. And that's where this falls apart. While some people buy quality headphones, many will be using cheap, or rebranded low-quality headphones, like beats, or even no-name headphones.

One attack vector doesn't need to cover everyone. Developing many attack vectors as possible gives you the greatest chance that one of them will work against a particular target. As an example, lets say that a particular organization has taken a number of standard precautions to prevent audio from being recorded surreptitiously. They've banned cell phones and chosen computers without internal mics. The ability to rec…

> The reason Sennheiser's worked so well is probably because they have a large speaker

The reason I’m singling out beats, and a few other cheap headphones is because those tend to add a DSP to boost the bass.

That’s why it wouldn’t work with them.

Re: Headphones can be hijacked to surreptitiously record audio

#125

Post by bigiain »

ptaipale wrote: post #117
telekid wrote: post #115

Earlier quoted context omitted.

How do you dial a zero? Edit: Just realized why a zero is in the '10' position on a rotary phone. Huh.

Yes, except in the Swedish phones, where the numbering starts from 0. So dialing 0 would make 1 pulse, dialing 1 would make 2 pulses, and dialing 9 would make 10 pulses.

That would have confused the guys in The Wire who eventually figured out the bad guys "jump 5" phone number encoding...

Re: Headphones can be hijacked to surreptitiously record audio

#126

Post by bigiain »

mountaineer22 wrote: post #112
bcheung wrote: post #83

Here's a neat party trick for you. I had a MacGyver moment in the past where I made a phone call with only are pair of old earbuds and a phone cord (no switches, no dial pad). A speaker is basically the same thing as a microphone in reverse. Normally it takes an electrical signal to move a physical element that creates the sound waves. But you can also move the element and it will generate an electrical signal. To di…

Did you know you can use a DC motor as a speaker, too? I have not tried using a motor as a mic.

AC motors as well. Lots of brushless quadcopter motor controllers buzz out diagnostic/startup tones from the motors as they power up.

Re: Headphones can be hijacked to surreptitiously record audio

#127

Post by qb45 »

wallacoloo wrote: post #110
janci wrote: post #76

Earlier quoted context omitted.

I think the opposite. Speakers are driven by an amplifier that will not let the audio in reverse, even if the soundcard output was switched to act as an input.

But might there be sufficient coupling between the amplifier's output and its input, such that driving the output pins via speaking into the speaker can produce a voltage on what is usually the input line to the amplifier? I suspect it may be possible, depending on what the firmware allows - amplifier circuitry often utilizes feedback in some form or another, which is essentially coupling the output to the input. And…

This could totally work in this kind of circuit for example:

https://en.wikipedia.org/wiki/Operational_amplifier_applicat...

While I have seen a soundcard using two such inverting stages in series for headphone output, in laptops dedicated chips are more common which probably don't have such strong coupling. But better safe than sorry if the NSA is after you :)

Re: Headphones can be hijacked to surreptitiously record audio

#129

Post by bmm6o »

bigiain wrote: post #125
ptaipale wrote: post #117

Earlier quoted context omitted.

Yes, except in the Swedish phones, where the numbering starts from 0. So dialing 0 would make 1 pulse, dialing 1 would make 2 pulses, and dialing 9 would make 10 pulses.

That would have confused the guys in The Wire who eventually figured out the bad guys "jump 5" phone number encoding...

The plot point in question was that they were encoding the phone number when leaving it as a callback number. Pulse dialing wouldn't have come into it.

Re: Headphones can be hijacked to surreptitiously record audio

#130

Post by qb45 »

detaro wrote: post #123
mikey_p wrote: post #122

Earlier quoted context omitted.

This exploit only works with analog headphones. They don't solve anything.

You won't get any signal back through an amplifier between the ouput (now input) and the headphones, so yes, adding one helps.

This ought to be true in most HP amps out there but there may be exceptions and possibly (I wonder if anybody ever investigated it?) some parasitic coupling too.

https://news.ycombinator.com/item?id=13014435#13018118

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