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

Generally speaking, inter-frame video compression uses an amount of data directly related to the amount that things change from one frame to the next. So while noise like leaves moving shows up as small changes moment to moment, larger changes are still realistically visible.

My younger years spent screwing around with video for a hobby are coming back to me now.

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

Well, It assumes that the amount of delta you can create in the transmitted image is sufficiently large that you can discern it from other sources of random variation in the image. So if the drone is moving around dramatically and there are huge deltas in the image, making your windows opaque / translucent repeatedly may not be sufficient signal. But if the drone is observing a dark compound and you flash lights everywhere repeatedly, it might not matter that the drone is moving around a lot - there might still be a dramatic change in the data transmitted by the drone.

Ultimately you're putting some signal into a potentially noisy channel and trying to reconstruct whether or not your observations contain that signal. The example is simple enough that normal human eyeballs looking at the output can detect it. Using more sophisticated techniques might be able to tease out smaller signals from noisier channels.

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.

Yes, just like anything...but it comes with a trade off.

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.

Indeed. However, it is a very good practical example of why encryption alone doesn't do much. (If the attacker can measure your data stream, they can make statistical assumptions and pull a lot of useful data out without breaking the encryption).

Perhaps we could at least say it's not novel/new?

What grabs the attention is isn't so much the procedure or technology itself, but the narrative that we're in a future where this kind of thing might be genuinely useful to somebody someday.

Perhaps, how I said that was a bit ambiguous/unclear. However, the article is calling it clever. The research demonstrates a weakness with the communication layer. Just because it applies to drones(insert buzz word) does not make it a novel idea. I just find it funny that Wired is writing about it since it deals with drones, but I have read multiple other papers on the mis-application of compression and cryptography. Finding, flaws is important, I just feel like the article was kinda over selling the concept.

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

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.

Buffered transmission is unlikely to help; after all, the surveillance target could store the received stream and look for patterns - it would only delay detection for the length of the buffer (which often would need to be kept short due to the real-time nature of much surveillance.

Granted, you could obfuscate things by varying the buffer length and padding the data stream (as suggested near the end of the article) - but at some point, a high-value surveillance target will probably just assume that a nearby drone is probably not operated by an avid bird-watcher or something like that and just blast the drone out of the sky. (Preferably using a laser or better still lots and lots of microwave RF - tends to get the surroundings less aggravated than using a shotgun...)

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.

Compress, and then encrypt can be quite devastating if the attacker can insert data into the encrypted payload.

For instance, let's say I can insert any word into an encrypted message. Let's say I insert the word "THE". I can compare the size of the two messages one with the inserted "THE", and the one without. If the size instead of increasing by three bytes increases by less than three. I can be certain the word "THE" is in the message or at least some of the characters. I can keep doing this till I can extract useful information out the message.

This is just the same thing. Video that is static compresses well, but video with lots of change does not compress as well.

So the camera basically let's you insert extra information into the encrypted data stream. Based of the changing size it leaks info. This one is quite simple. It just tells you where the camera is looking, making the scene more dynamic. However, the issue of compression and encryption applies to much more than just drones.

Got it - thank you.