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A proof-of-concept system for counter-surveillance against spy drones

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Re: A proof-of-concept system for counter-surveillance against spy drones

#31

Post by m4x »

callumprentice wrote: post #27

I expect image detection in a video stream is pretty advanced these days but I'd imagine you'd need to rotate the image being recorded 3D space to match the plane of the window so you can compare them both? If you know the position of the drone relative to the window, that's doable. Maybe the algorithms are clever enough to account for that these days. Interesting article - thanks for sharing.

Their technique doesn't actually do any image analysis at all, since the video stream from the drone is encrypted and they can't view it.

Rather, they monitor the bitrate of the video stream and exploit the fact that static/unchanging scenes compress well and have a low bitrate while scenes which are changing have a higher bitrate. They then deliberately change the scene (by blacking out a window) and see whether the bitrate of the video stream increases.

If there's a strong correlation between blacking out the window and changes in bitrate, they can conclude the drone is observing their window.

Re: A proof-of-concept system for counter-surveillance against spy drones

#32

Post by [deleted] »

cavanasm wrote: post #5
DannyB2 wrote: post #3

Earlier quoted context omitted.

The key insight is that the drone should store the video to local storage for later (1) recovery or (2) buffered encrypted transmission to the mother ship which would eliminate the leakage of clues about what subject is being spied upon.

The problem with that is the video feed is being actively used. If you want to know where someone is going, you can't just make your drone fly around randomly for hours recording video of the area you think they're in, you have to visually acquire your target, and then follow them.

[deleted]

Re: A proof-of-concept system for counter-surveillance against spy drones

#33

Post by _jgvg »

wyc wrote: post #28
personjerry wrote: post #19

My tl;dr understanding: Drones send video back to operator. Video is typically compressed so that it only updates part of the picture that have changed. Even if the video is encrypted, the researchers are able to measure the bitrate. Thus when the researchers make a significant change like putting a board against a window, and seeing if the traffic increases, the researchers can determine whether the drone is looking…

Couldn't this be bypassed by regulating a drone's bitrate to a constant steady flow? The sacrifice will be either video quality or freshness of data, but it would be a straightforward way get past that protection.

Or and even easier way: just have the drone fill up the stream with random data so that the data stream never goes "quiet" when the image is mostly unchanged.

No sacrificing video quality or freshness required.

Re: A proof-of-concept system for counter-surveillance against spy drones

#35

Post by yarg »

DannyB2 wrote: post #3
alistproducer2 wrote: post #2

>In other words, they can see what the drone sees, pulling out their recognizable pattern from the radio signal, even without breaking the drone's encrypted video. The most interesting part of this is how encrypted traffic leaks enough info to be reliably analyzed. Really cool stuff.

The key insight is that the drone should store the video to local storage for later (1) recovery or (2) buffered encrypted transmission to the mother ship which would eliminate the leakage of clues about what subject is being spied upon.

Buffering doesn't eliminate the VBR issue, it just obfuscates it in a breakable way.

The fix is a constant bitrate with a sensible block cipher mode.

Re: A proof-of-concept system for counter-surveillance against spy drones

#36

Post by godelski »

Sargos wrote: post #20
personjerry wrote: post #19

My tl;dr understanding: Drones send video back to operator. Video is typically compressed so that it only updates part of the picture that have changed. Even if the video is encrypted, the researchers are able to measure the bitrate. Thus when the researchers make a significant change like putting a board against a window, and seeing if the traffic increases, the researchers can determine whether the drone is looking…

I'm assuming this is predicated on the drone being absolutely still and that nothing in the scene (leaves on trees) is moving? Is that even realistic?

If you do a regular sequence of major changes, you could pick that signal out. This would create a larger and more regular signal in the data than the random noise from leaves. I don't think you could accurately predict observation with just one set of environmental changes.

Re: A proof-of-concept system for counter-surveillance against spy drones

#37

Post by FabHK »

gruez wrote: post #18
zaksoup wrote: post #7

What's really interesting to me here is the watermarking part of this. I imagine a future where everybody has little IR pins on their shoulder and phones scanning encrypted traffic for their watermark...

it doesn't work if everybody's doing it. your pin's flashing will get drowned out in the noise of everyone else's pin.

well, you might be able to recover it using something akin to CDMA.

Re: A proof-of-concept system for counter-surveillance against spy drones

#38

Post by godelski »

kmm wrote: post #25
Sargos wrote: post #20

Earlier quoted context omitted.

I'm assuming this is predicated on the drone being absolutely still and that nothing in the scene (leaves on trees) is moving? Is that even realistic?

Shouldn't simple linear movement of a scene still compress really well?

Yes. The compression works by analyzing changes in the screen. A simple example of this would be if you are displaying data. Say you are taking real time data and it is scrolling across the screen. Your display moves the data to the left, drops off what moved out of the frame, and adds what is new. Pictures are more complex, but the idea is the same. Only take what is new.

Re: A proof-of-concept system for counter-surveillance against spy drones

#39

Post by Drakim »

_jgvg wrote: post #33
wyc wrote: post #28

Earlier quoted context omitted.

Couldn't this be bypassed by regulating a drone's bitrate to a constant steady flow? The sacrifice will be either video quality or freshness of data, but it would be a straightforward way get past that protection.

Or and even easier way: just have the drone fill up the stream with random data so that the data stream never goes "quiet" when the image is mostly unchanged. No sacrificing video quality or freshness required.

So you compress the video to a smaller size, and then fill in the bandwidth you saved with random data?

Why compress at all? Wouldn't just having a pixel perfect stream solve the same issue and give better quality video?

Re: A proof-of-concept system for counter-surveillance against spy drones

#40

Post by godelski »

alistproducer2 wrote: post #2

>In other words, they can see what the drone sees, pulling out their recognizable pattern from the radio signal, even without breaking the drone's encrypted video. The most interesting part of this is how encrypted traffic leaks enough info to be reliably analyzed. Really cool stuff.

From my limited knowledge of encryption, this is why you don't compress before you encrypt. So if I understand the following article correctly, this kind of attack is well known. https://blog.appcanary.com/2016/encrypt-or-compress.html
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