4 ms·

If it is possible to strip the private key, e.g. by re-encoding, then an intelligent and determined leaker would simply do that before distribution. They likely

by plus 9y ago

If it is possible to strip the private key, e.g. by re-encoding, then an intelligent and determined leaker would simply do that before distribution. They likely won't be tempted to take the reward for themselves, given the consequences, and by stripping the private key they can prevent anyone else from claiming it. I suppose this would catch less savvy leakers, though. Edit: To be clear, I understand that digital watermarking techniques can be resilient to a simple re-encode, but since Custos is providing the tool to claim the reward for free to pirates, it should be possible to reverse-engineer the tool to identify and destroy the watermark.

dragonwriter 9y ago
Reading data out of an enclosed file is much less of a problem than altering that data without damaging the file. All you need for “screening” and “claiming” is to read out the keys and check if the funds have already been transferred out on the blockchain and, if not, transfer them out. There's no alteration to the file content involved. Destroying the keys requires altering the file while leaving it functional, which requires more than reverse engineering the tool, because the tool doesn't need that capacity.
- plus 9y ago
  My point is that if you can identify how the private key is stored in the video, then it should be possible to develop a strategy to destroy that data without damaging the integrity of the file. Presumably the key will be hidden in such a way that it won't be obvious to viewers (that is, it won't be a literal watermark). If that's true, then it should be possible to destroy the key without making the video quality noticeably worse, e.g. by selectively re-encoding certain parts of the video in a certain way that ensures destruction of the private key. Of course I'm speculating, because I don't know exactly how the private key is stored in the video, but video quality is a lot more robust to bit massaging than a hidden digital private key would be.
Retr0spectrum 9y ago
When they release the detection tool, and I reverse engineer it to produce a tool to set arbitrary watermarks on arbitrary video files, what would be the legality of releasing such a tool? Of course, pirates are unlikely to care about such legal issues, but I'm still curious if there are any.
- plus 9y ago
  >produce a tool to set arbitrary watermarks on arbitrary video files To what end? IANAL, so I can't comment on the legality of what you are suggesting.
gnode 9y ago
Custos could encode the key in any number of ways, while keeping them secret. They could later (maybe some time into the future) announce the method, and catch the source of the leak. As with any watermarking, the intention is not to make it physically impossible to make an unauthorised copy, but make it accountable. If the leaker can't be sure that they're aware of all the methods that could be used to catch them, they may decide against leaking their copy. One method may be to encode it cryptographically, in a way where it looks like noise until you have the key, similar to Code Division Multiple Access communication schemes.

by plus 9y ago

dragonwriter 9y ago

Reading data out of an enclosed file is much less of a problem than altering that data without damaging the file. All you need for “screening” and “claiming” is to read out the keys and check if the funds have already been transferred out on the blockchain and, if not, transfer them out. There's no alteration to the file content involved. Destroying the keys requires altering the file while leaving it functional, which requires more than reverse engineering the tool, because the tool doesn't need that capacity.

plus 9y ago
My point is that if you can identify how the private key is stored in the video, then it should be possible to develop a strategy to destroy that data without damaging the integrity of the file. Presumably the key will be hidden in such a way that it won't be obvious to viewers (that is, it won't be a literal watermark). If that's true, then it should be possible to destroy the key without making the video quality noticeably worse, e.g. by selectively re-encoding certain parts of the video in a certain way that ensures destruction of the private key. Of course I'm speculating, because I don't know exactly how the private key is stored in the video, but video quality is a lot more robust to bit massaging than a hidden digital private key would be.

Retr0spectrum 9y ago

When they release the detection tool, and I reverse engineer it to produce a tool to set arbitrary watermarks on arbitrary video files, what would be the legality of releasing such a tool? Of course, pirates are unlikely to care about such legal issues, but I'm still curious if there are any.

plus 9y ago
>produce a tool to set arbitrary watermarks on arbitrary video files To what end? IANAL, so I can't comment on the legality of what you are suggesting.

gnode 9y ago

Custos could encode the key in any number of ways, while keeping them secret. They could later (maybe some time into the future) announce the method, and catch the source of the leak. As with any watermarking, the intention is not to make it physically impossible to make an unauthorised copy, but make it accountable. If the leaker can't be sure that they're aware of all the methods that could be used to catch them, they may decide against leaking their copy. One method may be to encode it cryptographically, in a way where it looks like noise until you have the key, similar to Code Division Multiple Access communication schemes.