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A comment on Apple's T2 chip will prevent hackers from eavesdropping on your microphone. Parent comment

Re:Apple's T2 chip will prevent hackers from eavesdropping o... by newnewpdro on Sunday November 04, 2018 @05:20PM (#18378365)
> I would love to see a light come on if the camera or microphone is receiving power, and then only turn on power to these devices when a program requests it.

Isn't the microphone a simple passive device no different than a voice coil in a magnetic field? I don't think it's that simple, since it won't be powered.

My understanding is that there's often a reconfigurable circuit in the sound chip which determines where the lines in and out are routed. So even if you've physically disconnected the microphone, but left internal speakers connected, it's possible to turn the speakers into a microphone via software alone.

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Re:Apple's T2 chip will prevent hackers from eavesdropping o... by bigiain on Sunday November 04, 2018 @05:36PM (#18378427)
There's at least a pre amp and a d/a converter that the mic needs to have powered up and running before any of it's signal can be used by the rest of the computer.
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Re:Apple's T2 chip will prevent hackers from eavesdropping o... by newnewpdro on Sunday November 04, 2018 @05:46PM (#18378470)
Which will all be inside an IC, away from the microphone.

So what, does the light turn on whenever the entire IC sees power? Because if it relies on a signal from within the software-controlled IC, that's not exactly trivial to audit.

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Re:Apple's T2 chip will prevent hackers from eavesdropping o... by XMPPwocky on Sunday November 04, 2018 @06:16PM (#18378584)
The trivial solution would be a LED + resistor just wired across the mic's power rails.
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Re:Apple's T2 chip will prevent hackers from eavesdropping o... by newnewpdro on Sunday November 04, 2018 @07:13PM (#18378829)
When the microphone is a passive connected to a multifunction IC there's no such power rail.
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Re:Apple's T2 chip will prevent hackers from eavesdropping o... by justtopost on Sunday November 04, 2018 @09:10PM (#18379340)
Most laptop mics are condenser electret mics which usually use a small dc current, although not always.
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Re:Apple's T2 chip will prevent hackers from eavesdropping o... by newnewpdro on Monday November 05, 2018 @12:07AM (#18380008)
Not the last time I went down this road hardening a Thinkpad, see Step 6 at [1] (not my site). I haven't bothered with any smartphones yet, so I can't speak to what they tend to use for a mic. But if I carried one I'd definitely rip out all the voice coils and rely on a pair of headphones w/integrated mic for voice comms to mitigate potential for eavesdropping.

[1] https://blog.patternsinthevoid.net/replacing-a-thinkpad-x60-...

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Re:Apple's T2 chip will prevent hackers from eavesdropping o... by colejohnson66 on Monday November 05, 2018 @07:31AM (#18381772)
When replacing the lightning assembly on my iPhone 6, I noticed that the microphone looks passive. Here’s a photo[0]; It’s the little bronze(?) square next to the headphone jack.

[0]: https://www.ifixit.com/Store/iPhone/iPhone-6-Lightning-Conne...

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