From: (Anonymous)
"An attacker can "turn off" your TV, reconfigure the internal speaker output as an input and listen to you on your "microphoneless" TV"

Are you actually serious? I don't want to sink to your level of oversimplification, but on very loose terms, generally, a speaker will be driven by an amp, which will in turn be driven by a DAC, i.e. a piece of silicon that makes analogue signals out of bits.

By contrast, a microphone will be feeding an ADC - something that makes bits out of analogue signals. It's pretty much the opposite of the bidirectional data flow you are implying is possible. Sure it might be part of a bigger SoC but it will still be incapable of driving a speaker for sure.

I don't understand what could motivate someone to make this point, other a complete lack of understanding of basic electronic engineering. Look at a phone schematic. Show me some code for an Android phone that allows the speaker to be used a mic. I have respect for you as an author, but this point is stupid, no other way to describe it.

Lastly, even if your absurd point was valid, and it was possible to just start using a speaker as a mic arbitrarily, have you ever tried using a speaker as a mic, sure, it might "work" but the speaker will have very unfavourable audio characteristics when used as a mic, and you will capture sound, but getting meaningful information out of it, e.g. a conversation, is a very different problem, one which you won't be able to solve due to physical limitations of the device.

TLDR: prove that there exist a significant number of devices where the speaker can be reconfigured to act as a mic in practise or GTFO
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Matthew Garrett

About Matthew

Power management, mobile and firmware developer on Linux. Security developer at Google. Member of the Free Software Foundation board of directors. Ex-biologist. @mjg59 on Twitter. Content here should not be interpreted as the opinion of my employer.

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