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How I discovered a hidden microphone on a Chinese NanoKVM

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Re: How I discovered a hidden microphone on a Chinese NanoKVM

#21

Post by Y_Y »

ndsipa_pomu wrote: post #13
tayiorrobinson wrote: post #3

To be fair, the microphone _is_ listed on the specsheet of the LicheeRV Nano https://wiki.sipeed.com/hardware/en/lichee/RV_Nano/1_intro.h... I assume they didn't intend to put a mic on the KVM product, but they wanted to make a KVM product, already had this SBC product, which reusing their existing stock of helped keep cost low. Should they have been more up front about it it? Sure, and it's not great that they had a…

It doesn't strike me as that useful to have a hidden microphone in a KVM product as most of the time, they're going to be stuck in server rooms with just lots of fan noise to record. Far more of an issue would be any kind of keylogger built into the software, which is why it's best to go for devices that support open source software.

just fan noise?

https://arxiv.org/abs/1606.05915

Any signal that you can modulate can be an exfiltration channel, and fan noise is no different.

Re: How I discovered a hidden microphone on a Chinese NanoKVM

#22

Post by mystraline »

nottorp wrote: post #18
kenjackson wrote: post #9

Earlier quoted context omitted.

What was wrong with the above paragraph?

Let's see: 1. It lacks systemd and apt. systemd is so resource hungry that i'm sure they removed it to reduce the RAM bill. Apt... why install apt if the distro has a different means of updating? 2. While these are useful for debugging and development, they are also hacking tools that can be dangerously exploited. This is purely fear mongering. Even the shell could be a "hacking tool that can be dangerously exploited…

Cat is a hacking tool cause you can see the contents of /proc/kcore?

Cp is a hacktool cause bad files can be copied?

Grep is a hacktool cause only monster hackers use regex?

(This is obvious sarcasm)

Re: How I discovered a hidden microphone on a Chinese NanoKVM

#23

Post by Y_Y »

Workaccount2 wrote: post #12
mannanj wrote: post #4

any speaker can be tapped into as a microphone by a motivated government.

No, because the drive circuit for a speaker is the opposite of the circuit for a microphone. The output stage of a speaker amplifier is just that, an output . The only way to record audio from a speaker, which is totally possible, is to have also purposely built an input stage also attached to the speaker. Which at that point you might as well just use a microphone... Audio input and output are not reversible.

I don't know what you mean here, I can plug a speaker into my mic slot and use that to record, just as plugging a mic into the speaker slot gives a (crappy) speaker.

Re: How I discovered a hidden microphone on a Chinese NanoKVM

#24

Post by ErroneousBosh »

i_am_proteus wrote: post #14
ndsipa_pomu wrote: post #13

Earlier quoted context omitted.

It doesn't strike me as that useful to have a hidden microphone in a KVM product as most of the time, they're going to be stuck in server rooms with just lots of fan noise to record. Far more of an issue would be any kind of keylogger built into the software, which is why it's best to go for devices that support open source software.

It is possible to keylog via audio. https://ieeexplore.ieee.org/abstract/document/10190721

A long time ago (maybe in the mid-90s) I knew an elderly radio amateur who could not just "copy" CW by ear, but also RTTY. He could also pretty much tell what a teleprinter was printing just by listening to the noises it made, like he'd be facing away from it on the other side of the room reading out entire words from what was coming through.

Apparently in the 50s when he did his National Service he'd been in the Signals but "not in the regiment that's on his papers", make of that what you will.

I have noticed that with PSK modes and particularly PSK31 you can hear "CQ CQ CQ" as a distinctive pattern much in the same way as it is with CW.

IBM spent a fortune developing ATM keypads that - when correctly mounted - had keys that made the exact same noise no matter how you pressed them or how worn they were.

So I don't doubt that someone suitably clever could extract audio from a room and work out what was being typed.

Re: How I discovered a hidden microphone on a Chinese NanoKVM

#25

Post by stragies »

Aachen wrote: post #8
mannanj wrote: post #4

any speaker can be tapped into as a microphone by a motivated government.

From a hardware point of view I've also noticed that speakers work like poor microphones (and LEDs like poor solar panels / light sensors), but is there any way to actually make this work on most devices without physically changing wiring? If the circuits aren't made to take measurements (or the software can't get at the readings) but only set a voltage on the wires, there wouldn't be a way to (ab)use this. I don't k…

Many a soundcard supports changing jack "direction". Here's a StackExchange answer from 2012, on how to do it with the GUI tool `hdajackretask` : https://askubuntu.com/a/911961

Re: How I discovered a hidden microphone on a Chinese NanoKVM

#28

Post by stragies »

Workaccount2 wrote: post #12
mannanj wrote: post #4

any speaker can be tapped into as a microphone by a motivated government.

No, because the drive circuit for a speaker is the opposite of the circuit for a microphone. The output stage of a speaker amplifier is just that, an output . The only way to record audio from a speaker, which is totally possible, is to have also purposely built an input stage also attached to the speaker. Which at that point you might as well just use a microphone... Audio input and output are not reversible.

on many cards they are, check out the tool `hdajackretask` from package `alsa-gui-tools`.

Re: How I discovered a hidden microphone on a Chinese NanoKVM

#29

Post by whalesalad »

Milpotel wrote: post #5

> [...] and runs a heavily stripped-down version of Linux that lacks systemd and apt. And these are just a few of the issues. ?!

I don’t see this as noteworthy myself. It’s expected on a small embedded device such as this. You’re usually lucky to have busybox.

Re: How I discovered a hidden microphone on a Chinese NanoKVM

#30

Post by f1shy »

ErroneousBosh wrote: post #24
i_am_proteus wrote: post #14

Earlier quoted context omitted.

It is possible to keylog via audio. https://ieeexplore.ieee.org/abstract/document/10190721

A long time ago (maybe in the mid-90s) I knew an elderly radio amateur who could not just "copy" CW by ear, but also RTTY. He could also pretty much tell what a teleprinter was printing just by listening to the noises it made, like he'd be facing away from it on the other side of the room reading out entire words from what was coming through. Apparently in the 50s when he did his National Service he'd been in the Sig…

Do you have a pointer to learn more about the ATM keyboards? I would love to learn more about it
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