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Comment by duxup | Hacker News Reader

I wish we had a physical switch that cut power to the camera and mic...

I worked on some old networking equipment a while back that had a physical fail over switch. If you opened the cover you could watch the connection switch, fun stuff. Also very effective.

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The description makes it sound like Apple is using a hardware interlock that I'd assume cuts power to the microphone via a MOSFET when the lid is closed. That's pretty much the same thing, just with a solid state switch instead of a mechanical contact.

That's pretty cool.

It is pretty cool indeed, however keep in mind that's just standard component in circuits to turn signals on and off. It is just a PNP or NPN transistor. Everyone makes use of it.

To be clear too, I'm just speculating about that part. The only thing this document says is that "This disconnect is implemented in hardware alone, and therefore prevents any software, even with root or kernel privileges in macOS, and even the software on the T2 chip, from engaging the microphone when the lid is closed." That implies to me that they are using some form of physical interlock (probably a magnet and Hall-effect sensor), and that they use this to completely disable the microphone. The most obvious way to me to do that in this case would be to cut the power with a transistor, but in principle there are a number of other ways it could be achieved.

I think it makes sense to assume they have a hall-effect sensor and a MOSFET but of course maybe they combined both in a single package.

Thinking how a hall-effect sensor works, perhaps it would be possible to embed it in a wafer with some gates and you're done.

Purism laptops have hardware kill switches for camera/mic and wifi/bluetooth.

https://puri.sm/products/librem-13/

Unfortunately it has much weaker specs. No thunderbolt, only dual core CPU, slow Wi-Fi. They didn't even care enough to tell us the screen resolution, which is at least to me an important thing to know before buying.

Newer Thinkpads have a shutter to cover the camera, but mic still works when covered.

https://www.businessinsider.com/lenovo-thinkshutter-laptops-...

Yeah I got some handy shutters from some conferences, not a bad solution.

They say that "The camera is not disconnected in hardware because its field of view is completely obstructed with the lid closed."

And since the webcam in Macs electrically can't get power without also powering the green notification LED, it's impossible for malicious actors to activate the webcam silently while the lid is open.

Is that still true?

I read some time ago that the LED used to be hardware controlled, but switched to being software controlled at some point.

I wonder how long it will be until someone manages to figure out how to use image processing to read the noise seen by the camera sensor while the lid is closed and turn it into audio.

Kind of like this: http://news.mit.edu/2014/algorithm-recovers-speech-from-vibr...

That's certainly an interesting thought, but do note (from the linked article):

In some of their experiments, the researchers used a high-speed camera that captured 2,000 to 6,000 frames per second..

I haven't checked, but I would be surprised if Apple uses cameras that are capable of that as normal user-facing webcams in their laptops ...

Recovering meaningful audio signal (which usually has lots of data above 1 kHz) from the <100 Hz sampling done by a camera seems difficult, Nyquist and all, right?

From the next paragraph:

In other experiments, however, they used an ordinary digital camera. Because of a quirk in the design of most cameras’ sensors, the researchers were able to infer information about high-frequency vibrations even from video recorded at a standard 60 frames per second.

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