Tempest, it uhhhh finds a way.

4 months ago by einfach_orangensaft to c/cybersecuritymemes

I knew that it was possible to spy on CRT displays due to the signals they radiate, but apparently that is a problem with HDMI too.

Here a very interesting write up on how to extract frames from leaked RF from HDMI cables and using said RF to transmit a webcam stream even: https://www.windytan.com/...

Here a example of someone using HDMI RF to transmit LoRa signals: https://www.youtube.com/watch?v=HDbdAZd6cLw

This makes for a interesting attack vector for locating a user, if said user clicks on a video (or even a gif) that crafts LoRa frames to radiate from his HDMI and there is for example a Meshtastic receiver near by that relays those frames into a wider network.

There are ways to migrate this issue, for example using the encrypted version of HDMI usually used to enforce content copyright protection, or using a fiber optic HDMI cable (by now they are almost as cheap as the copper ones and are not restricted to a max lenght of 5m).

NaibofTabr 22 points 4 months ago

Would ferrite beads be a cheap and simple solution for this? You can buy them as clip-ons for cables that don't have them built in.

This makes for a interesting attack vector for locating a user, if said user clicks on a video (or even a gif) that crafts LoRa frames to radiate from his HDMI and there is for example a Meshtastic receiver near by that relays those frames into a wider network.

Also, I'm not sure I see the point of this... if you already know where the HDMI cable is with enough accuracy to collect low-power radio emissions, then you already know the user's location - they're probably pretty close to the monitor that the HDMI cable is plugged into.

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RustyNova 12 points 4 months ago

OH that's what those are. Always wondered wtf was that little bulb thing

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HAL_9_TRILLION 6 points 4 months ago

Also, I'm not sure I see the point of this... if you already know where the HDMI cable is with enough accuracy to collect low-power radio emissions, then you already know the user's location

Well the other half of it is that whatever media is being run through the cable is compromised so that it emits RF that is recognizable to a LoRa device. Such a device would think it was coming from another Meshtastic device and would therefore pick it up and broadcast it, which could serve to locate someone in a wide area.

So it's interesting, but it seems pretty niche. You can deliver compromised media to someone you can't locate AND they are a Meshtastic hobbyist... yeah not likely.

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RustyNova 11 points 4 months ago

Wtf. Hdmi is leaking redstone flux now!?

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daannii 10 points 4 months ago

When I was a kid , the house we had had this row of 3 rooms in the back. 9x9x9. There were 3 of us kids so we each had one of the rooms.

We had these old tvs people gave us.

I believe mine was black and white and the other two color but the point is they were old style tvs. Like from the 70s at earliest.

So in one of the rooms we had the TV hooked to a Nintendo.

Here is the bizarre thing. If you turned one of the TVs on in the room next to it, you could watch the Nintendo game being played. It only broadcast on one or 2 channels.

It was rough static quality. But seemed to stream to the other TV through the wall in real time. But no sound streamed. Just video.

They weren't connected in any way other than power outlet.

I remember us kids thought it was so cool and showed anyone who came over and we experimented to see how far away it would work. It didn't work if it was tv from room 1 and 3. But any other combination worked. We tried different things and found ways to increase the quality but I can't recall what we tried.

It also didn't stream to the tv in the living room. (A 90s tv).

We thought maybe it was cause of whatever these old tvs were made of. All that copper maybe worked like an antenna.

Dunno. We were kids. I still have no idea how it worked.

Considering I can't get steamlink to work for shit it would be nice if there was some alternative ways to send signals like that.

I thought maybe this story was related. And maybe someone could explain the phenomenon.

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BCsven 13 points 4 months ago

I assume its because the Nintendo back then probably had a switcher on the back of the TV to inject the display in your RF antenna coax. That coax was probably connected to your TV antenna, so you got low emission transmission.

A guess. And still pretty cool

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despoticruin 13 points 4 months ago

Close, the NES actually broadcasts a standard NTSC RF signal on its output. The old TVs were acting as a broadcast antenna for the others to pick up. You can do the same thing with some decent rabbit ears by just putting a paperclip into the center pin of the RF output on the side of the console. Don't play that way though, you would be technically operating a pirate TV station if you didn't have a license to broadcast on that channel. The NES should be a low enough output power that it doesn't matter either way.

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iocase 10 points 4 months ago

Fun fact: before superheterodyne radios were invented, you needed a license to operate a radio including just to plug it in and tune it.

The reason is simple regenerative radios back In the day were also transmitting a small amount of signal back when they were receiving a station. As a result, at least in the US you needed a radio operator's license to listen to a radio since you were technically transmitting.

Super heterodyne radios fixed this though by having extremely levels of sensitivity and basically now backfeed signal transmitted.

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despoticruin 3 points 4 months ago

I love seeing mentions of superHets in the wild. Back in my day we sparked car batteries across a measured loop of wire!

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daannii 2 points 4 months ago

Well the TVs only had one coaxial so maybe the receiver tv was hooked to an antenna (probably a set of rabbit ears) but the sender wouldn't have been.

I think we did try messing around with the antennas but it was so long ago I can't be sure. But maybe messing with them is what improved the signal. I do remember for sure we improved it.

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Viceversa 5 points 4 months ago

There are ways to migrate this issue

Why to migrate it?

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