4 ms·

Everyone in her claims that there are mechanisms to add non-visual watermarks into both video & audio, anyone have any suggestions as to what products / systems

by krob 11y ago

Everyone in her claims that there are mechanisms to add non-visual watermarks into both video & audio, anyone have any suggestions as to what products / systems to use so this can be implemented? Minus writing one yourself (like writing your own framework, you don't know all the gotcha's of an expert)

TazeTSchnitzel 11y ago
It's not a very compression-resistant approach and more sophisticated methods are usually used, but a simple one is using the low bits of colour channels. In a red pixel you have bits like so: RED GREEN BLUE 11111111 00000000 00000000 A change in the most significant bit of any of these colours would be massive. 01111111 is half as bright as 11111111. But a change in the least significant bit(s) is barely noticeable. You probably wouldn't notice the difference between 11111111 and 11111110, especially as you don't experience individual colour channels, you see a blended colour. And when you're looking at something with thousands of pixels you simply won't spot it. So, stick your secret message in the low bits: RED GREEN BLUE 11111XXX 00000XXX 00000XXX You now get 9 bits of data per pixel. Or less (for a less noisy image) or more (for a more noisy image). For a 640x480 image, you now have 345.6KB of data. And if you use encrypted data, it won't even seem like data if someone looks (plausible deniability). Just noise. Techniques like this were used on 4chan to hide child porn in high-resolution photographs. This the "mods are asleep, post hi-res" meme.
- CHY872 11y ago
  You don't get plausible deniability in any way. Turns out that the least significant bits of a pixel are not uniformly distributed. The obvious example of failure is that you expect more pixels with value 255 than 254, since any overexposure will be stuck at 255. The rest is obvious when you look at a histogram of pixel values; as the number of LSBs used increases you see the curve become stepped. LSB replacement steganography is easily detectable at about a ratio of about 0.01 bits per pixel. The smarter plan is to add or subtract 1 randomly (or do nothing) in order to match the LSB to what you want; this symmetry is harder to detect (but still very possible, the methods are just more complicated). The reason you encrypt the data is not just for data security, it is so that the embedder does not have to worry about the data that they are embedding screwing everything up. tl;dr LSB steganography does not give you any plausible deniability because it's really easy to detect in any type of image at very low embedding levels due to inherent limitations of the process. If you want to use it, you'd be safe with a single message at perhaps a level of 0.005 bits per pixel, but then in a ten megapixel image you'd get 150kB of data which hardly seems worth it when you have to transmit losslessly. Even then, you'd still be screwed at a theoretical level with Ker's square root law.
  - TazeTSchnitzel 11y ago
    Ah, I see. I hadn't thought of the 255 issue, in hindsight that seems obvious. Still, I think LSB replacement steganography is useful if only to provide an example of how it steganography can be done, even if it's not particularly sophisticated.
- TazeTSchnitzel 11y ago
  s/This the/Thus the/
shortkud 11y ago
These are products in use by the industry for video http://www.civolution.com/ http://www.civolution.com/ http://www.vobileinc.com/technology/ http://www.vobileinc.com/technology/

by krob 11y ago

TazeTSchnitzel 11y ago

It's not a very compression-resistant approach and more sophisticated methods are usually used, but a simple one is using the low bits of colour channels. In a red pixel you have bits like so: RED GREEN BLUE 11111111 00000000 00000000 A change in the most significant bit of any of these colours would be massive. 01111111 is half as bright as 11111111. But a change in the least significant bit(s) is barely noticeable. You probably wouldn't notice the difference between 11111111 and 11111110, especially as you don't experience individual colour channels, you see a blended colour. And when you're looking at something with thousands of pixels you simply won't spot it. So, stick your secret message in the low bits: RED GREEN BLUE 11111XXX 00000XXX 00000XXX You now get 9 bits of data per pixel. Or less (for a less noisy image) or more (for a more noisy image). For a 640x480 image, you now have 345.6KB of data. And if you use encrypted data, it won't even seem like data if someone looks (plausible deniability). Just noise. Techniques like this were used on 4chan to hide child porn in high-resolution photographs. This the "mods are asleep, post hi-res" meme.

CHY872 11y ago
You don't get plausible deniability in any way. Turns out that the least significant bits of a pixel are not uniformly distributed. The obvious example of failure is that you expect more pixels with value 255 than 254, since any overexposure will be stuck at 255. The rest is obvious when you look at a histogram of pixel values; as the number of LSBs used increases you see the curve become stepped. LSB replacement steganography is easily detectable at about a ratio of about 0.01 bits per pixel. The smarter plan is to add or subtract 1 randomly (or do nothing) in order to match the LSB to what you want; this symmetry is harder to detect (but still very possible, the methods are just more complicated). The reason you encrypt the data is not just for data security, it is so that the embedder does not have to worry about the data that they are embedding screwing everything up. tl;dr LSB steganography does not give you any plausible deniability because it's really easy to detect in any type of image at very low embedding levels due to inherent limitations of the process. If you want to use it, you'd be safe with a single message at perhaps a level of 0.005 bits per pixel, but then in a ten megapixel image you'd get 150kB of data which hardly seems worth it when you have to transmit losslessly. Even then, you'd still be screwed at a theoretical level with Ker's square root law.
- TazeTSchnitzel 11y ago
  Ah, I see. I hadn't thought of the 255 issue, in hindsight that seems obvious. Still, I think LSB replacement steganography is useful if only to provide an example of how it steganography can be done, even if it's not particularly sophisticated.
TazeTSchnitzel 11y ago
s/This the/Thus the/

shortkud 11y ago

These are products in use by the industry for video http://www.civolution.com/ http://www.civolution.com/ http://www.vobileinc.com/technology/ http://www.vobileinc.com/technology/