41 ms·

Without having read into this deeper, it sounds like someone could take an original video which has this code embedded as small fluctuations in luminance over t

Without having read into this deeper, it sounds like someone could take an original video which has this code embedded as small fluctuations in luminance over time and edit it or produce a new video, simply applying the same luminance changes to the edited areas/generated video, no? It seems for a system like this every pixel would need to be digitally signed by the producer for it to be non-repudiable.

crazygringo 1y ago
Exactly, that is my question too. If you can detect the lighting variations to read and verify the code, then you can also extract them, remove them, reapply to the edited version or the AI version... varying the level of global illumination in a video is like the easiest thing to manipulate. Although there's a whole other problem with this, which is that it's not going to survive consumer compression codecs. Because the changes are too small to be easily perceptible, codecs will simply strip them out. The whole point of video compression is to remove perceptually insignificant differences.
- janaagaard 1y ago
  As I understand it, the brilliant idea is that the small variantions in brightness of the pixels look just like standard noise. Distinguishing the actual noise from the algorithm is not possible, but it is still possible to verify that the 'noise' has the correct pattern.
  - cwmoore 1y ago
    Correct pattern for the correct time span matching random fluctuations in the electrical grid.
    - kumarvvr 1y ago
      I think that will be handled by the AC to DC conversion in most systems.
      - 4gotunameagain 1y ago
        Nope. Mains hum is picked up by microphones as well as light intensity: https://en.wikipedia.org/wiki/Electrical_network_frequency_analysis https://en.wikipedia.org/wiki/Electrical_network_frequency_a...
  - deleted 1y ago
    [deleted]
TeeMassive 1y ago
Not if you encode a cryptographic signature in the watermark
- yapyap 1y ago
  what would that change
  - zeta0134 1y ago
    The general idea is for the signature to be random each time, but verifiable. There are a bajillion approaches to this, but a simple starting point is to generate a random nonce, encrypt it with your private key, then publish it along with the public key. Only you know the private key, so only you could have produced the resulting random string that decodes into the matching nonce with the public key. Also, critically, every signature is different. (that's what the nonce is for.) If two videos appear to have the same signature, even if that signature is valid, one of them must be a replay and is therefore almost certainly fake. (Practical systems often include a generational index or a timestamp, which further helps to detect replay attacks.) I think for the approach discussed in the paper, bandwidth is the key limiting factor, especially as video compression mangles the result, and ordinary news reporters edit the footage for pacing reasons. You want short clips to still be verifiable, so you can ask questions like "where is the rest of this footage" or "why is this played out of order" rather than just going, "there isn't enough signature left, I must assume this is entirely fake."
    - SamBam 1y ago
      But the point is that you'd be extracting the nonce from someone else's existing video of the same event. If a celebrity says something and person A films a true video, and person B films a video and then manipulates it, you'd be able to see that B's light code is different. But if B simply takes A's lighting data and applies it to their own video, now you can't tell which is real.
      - DoctorOetker 1y ago
tripdout 1y ago
The code embedded into the luminosity is sampled from a distribution resembling the noise already present in the video. Plus, the code gives information about the frame it's embedded into, so you still have more work to do.
- mustyoshi 1y ago
  Doesn't this just fall apart if a video is reencoded? Something fairly common on all video platforms.
  - ramses0 1y ago
    Take a computer screen with a full wash of R, G, or B. Sync the RGB display with your 2FA token, but run it at 15FPS instead of one code per minute. Point the monitor at the wall, or desk, or whatever. Notice the radiosity and diffuse light scattering on the wall (and on the desk, and on the reflection on the pen cap, and on their pupils). Now you can take a video that was purported to be taken at 1:23pm at $LOCATION and validate/reconstruct the expected "excess" RGB data and then compare to the observed excess RGB data. What they say they've done as well is to not just embed a "trace" of expected RGB values at a time but also a data stream (eg: a 1FPS PNG) which kindof self-authenticates the previous second of video. Obviously it's not RGB, but "noise" in the white channels, and not a PNG, but whatever other image compression they've figured works well for the purpose. In the R, G, B case you can imagine that it's resistant (or durable through) most edits (eg: cuts, reordering), and it's interesting they're talking about detecting if someone has photoshopped in a vase full of flowers to the video (because they're also encoding a reference video/image in the "noise stream").
  - gorkish 1y ago
    No, unsafe-yt
lowbloodsugar 1y ago
Academics presenting the opening move in a game of white hat / black hat thinking the game is over after one turn.
Palmik 1y ago
The code could be cryptographically derived from the content of the video. For simplicy, imagine there are subtitles baked into the video and the code is cryptographically derived from those.
gorkish 1y ago
So what if your adversary relays your encrypted message along another channel?

crazygringo 1y ago

Exactly, that is my question too. If you can detect the lighting variations to read and verify the code, then you can also extract them, remove them, reapply to the edited version or the AI version... varying the level of global illumination in a video is like the easiest thing to manipulate. Although there's a whole other problem with this, which is that it's not going to survive consumer compression codecs. Because the changes are too small to be easily perceptible, codecs will simply strip them out. The whole point of video compression is to remove perceptually insignificant differences.

janaagaard 1y ago
As I understand it, the brilliant idea is that the small variantions in brightness of the pixels look just like standard noise. Distinguishing the actual noise from the algorithm is not possible, but it is still possible to verify that the 'noise' has the correct pattern.
- cwmoore 1y ago
  Correct pattern for the correct time span matching random fluctuations in the electrical grid.
  - kumarvvr 1y ago
    I think that will be handled by the AC to DC conversion in most systems.
    - 4gotunameagain 1y ago
      Nope. Mains hum is picked up by microphones as well as light intensity: https://en.wikipedia.org/wiki/Electrical_network_frequency_analysis https://en.wikipedia.org/wiki/Electrical_network_frequency_a...
- deleted 1y ago
  [deleted]

TeeMassive 1y ago

Not if you encode a cryptographic signature in the watermark

yapyap 1y ago
what would that change
- zeta0134 1y ago
  The general idea is for the signature to be random each time, but verifiable. There are a bajillion approaches to this, but a simple starting point is to generate a random nonce, encrypt it with your private key, then publish it along with the public key. Only you know the private key, so only you could have produced the resulting random string that decodes into the matching nonce with the public key. Also, critically, every signature is different. (that's what the nonce is for.) If two videos appear to have the same signature, even if that signature is valid, one of them must be a replay and is therefore almost certainly fake. (Practical systems often include a generational index or a timestamp, which further helps to detect replay attacks.) I think for the approach discussed in the paper, bandwidth is the key limiting factor, especially as video compression mangles the result, and ordinary news reporters edit the footage for pacing reasons. You want short clips to still be verifiable, so you can ask questions like "where is the rest of this footage" or "why is this played out of order" rather than just going, "there isn't enough signature left, I must assume this is entirely fake."
  - SamBam 1y ago
    But the point is that you'd be extracting the nonce from someone else's existing video of the same event. If a celebrity says something and person A films a true video, and person B films a video and then manipulates it, you'd be able to see that B's light code is different. But if B simply takes A's lighting data and applies it to their own video, now you can't tell which is real.
    - DoctorOetker 1y ago

tripdout 1y ago

The code embedded into the luminosity is sampled from a distribution resembling the noise already present in the video. Plus, the code gives information about the frame it's embedded into, so you still have more work to do.

mustyoshi 1y ago
Doesn't this just fall apart if a video is reencoded? Something fairly common on all video platforms.
- ramses0 1y ago
  Take a computer screen with a full wash of R, G, or B. Sync the RGB display with your 2FA token, but run it at 15FPS instead of one code per minute. Point the monitor at the wall, or desk, or whatever. Notice the radiosity and diffuse light scattering on the wall (and on the desk, and on the reflection on the pen cap, and on their pupils). Now you can take a video that was purported to be taken at 1:23pm at $LOCATION and validate/reconstruct the expected "excess" RGB data and then compare to the observed excess RGB data. What they say they've done as well is to not just embed a "trace" of expected RGB values at a time but also a data stream (eg: a 1FPS PNG) which kindof self-authenticates the previous second of video. Obviously it's not RGB, but "noise" in the white channels, and not a PNG, but whatever other image compression they've figured works well for the purpose. In the R, G, B case you can imagine that it's resistant (or durable through) most edits (eg: cuts, reordering), and it's interesting they're talking about detecting if someone has photoshopped in a vase full of flowers to the video (because they're also encoding a reference video/image in the "noise stream").
- gorkish 1y ago
  No, unsafe-yt

lowbloodsugar 1y ago

Academics presenting the opening move in a game of white hat / black hat thinking the game is over after one turn.

Palmik 1y ago

The code could be cryptographically derived from the content of the video. For simplicy, imagine there are subtitles baked into the video and the code is cryptographically derived from those.

gorkish 1y ago

So what if your adversary relays your encrypted message along another channel?