5 ms·

DRM is always pointless because the content has to be converted to analog form at some point. So, it gets decrypted in the DistrustZone, decompressed, then encr

DRM is always pointless because the content has to be converted to analog form at some point. So, it gets decrypted in the DistrustZone, decompressed, then encrypted again before it goes over HDCP to your display, which then decrypts it to show it on the screen. Couldn't you capture the LVDS signal that the display panel receives? And even if you don't do that, isn't every version of HDCP cracked already so you could use a capture card instead?

wmf 5y ago
The last bastion of DRM is forensic watermarking (so they can trace the leaked video back to your device) and key revocation (so your device won't play any new content). These techniques are so complex that they aren't used much.
- grishka 5y ago
  So they trace the ripped video file to a particular throwaway account that was registered with a prepaid card, then what? And if you're determined enough, you could as well rip multiple copies on behalf of multiple accounts and average out the pixel colors.
  - wmf 5y ago
    The idea is to revoke the device, not the account.
  - throwaway525142 5y ago
    > you could as well rip multiple copies on behalf of multiple accounts and average out the pixel colors. Can you show that this can reliable get rid of the fingerprinting? This particular method could be countered by only including the fingerprint info in a few random frames, then you'd be able to retrieve the account info of all the accounts that participated in ripping. I don't think finding a method to counter any sort of fingerprinting is as easy as "just averaging the pixels".
    - azalemeth 5y ago
      It's my understanding that most schemes actually use very low frequency encoding with a large amount of error robustness built in (probably involving Haar wavelets) in order to maximize the probability that it survives re-encoding. Still, these schemes are not faultless: if you have two devices, and are knowledgeable enough to break the DRM twice for the same content, you're probably smart enough to take the md5 and shasum of the resulting bitstreams and diff them. Any discrepancy results in signal processing transforms until they have the same hashes...
      - baybal2 5y ago
        If they can get the content key out of TZ, they don't even need the per-device key, and TZ based decoder anymore. They just straight decrypt any files, which were at some point laying in the open on CDNs. I believe, sooner or later it will come to the point when the only way left for DRMed content to work will be to have each stream individually encrypted, and watermarked at the backend at an enormous computational expense.
      - mjevans 5y ago
        You'd ideally do this for 3+ devices and just majority vote on every framelocked frame; take the mean average if there isn't a median.
- conradev 5y ago
  Isn't it also incompatible with the distribution model? Because personalizing video for every customer is hard to scale for companies that rely on reducing cloud costs
  - wmf 5y ago
    The watermarking is done during playback, not distribution.
    - sblom 5y ago
      I took conradev to mean "the model of distributing the same content to everyone via traditional (passive) CDN". Movie theater watermarking is done during playback, but if Netflix was going to do watermarking, it would have to be done prior to delivery of streamed bits or it would be susceptible to the same "it's just software" attacks as any other local software-only approach to DRM.
      - wmf 5y ago
        Is Widevine L1 "just software"? If its key distribution can somehow remain uncracked for years then maybe it could also do client-side watermarking.
  - SilverRed 5y ago
    It's mostly done for review copies of content where only a handful of reviewers have the content.
- Wowfunhappy 5y ago
  Watermarking is the kind of DRM I'm 100% okay with. Please, sell me a watermarked but DRM-free video file that I can use with any player on any device. If I share it, you'll know it was me, but otherwise I have complete freedom. Win-win.

wmf 5y ago

The last bastion of DRM is forensic watermarking (so they can trace the leaked video back to your device) and key revocation (so your device won't play any new content). These techniques are so complex that they aren't used much.

grishka 5y ago
So they trace the ripped video file to a particular throwaway account that was registered with a prepaid card, then what? And if you're determined enough, you could as well rip multiple copies on behalf of multiple accounts and average out the pixel colors.
- wmf 5y ago
  The idea is to revoke the device, not the account.
- throwaway525142 5y ago
  > you could as well rip multiple copies on behalf of multiple accounts and average out the pixel colors. Can you show that this can reliable get rid of the fingerprinting? This particular method could be countered by only including the fingerprint info in a few random frames, then you'd be able to retrieve the account info of all the accounts that participated in ripping. I don't think finding a method to counter any sort of fingerprinting is as easy as "just averaging the pixels".
  - azalemeth 5y ago
    It's my understanding that most schemes actually use very low frequency encoding with a large amount of error robustness built in (probably involving Haar wavelets) in order to maximize the probability that it survives re-encoding. Still, these schemes are not faultless: if you have two devices, and are knowledgeable enough to break the DRM twice for the same content, you're probably smart enough to take the md5 and shasum of the resulting bitstreams and diff them. Any discrepancy results in signal processing transforms until they have the same hashes...
    - baybal2 5y ago
      If they can get the content key out of TZ, they don't even need the per-device key, and TZ based decoder anymore. They just straight decrypt any files, which were at some point laying in the open on CDNs. I believe, sooner or later it will come to the point when the only way left for DRMed content to work will be to have each stream individually encrypted, and watermarked at the backend at an enormous computational expense.
    - mjevans 5y ago
      You'd ideally do this for 3+ devices and just majority vote on every framelocked frame; take the mean average if there isn't a median.
conradev 5y ago
Isn't it also incompatible with the distribution model? Because personalizing video for every customer is hard to scale for companies that rely on reducing cloud costs
- wmf 5y ago
  The watermarking is done during playback, not distribution.
  - sblom 5y ago
    I took conradev to mean "the model of distributing the same content to everyone via traditional (passive) CDN". Movie theater watermarking is done during playback, but if Netflix was going to do watermarking, it would have to be done prior to delivery of streamed bits or it would be susceptible to the same "it's just software" attacks as any other local software-only approach to DRM.
    - wmf 5y ago
      Is Widevine L1 "just software"? If its key distribution can somehow remain uncracked for years then maybe it could also do client-side watermarking.
- SilverRed 5y ago
  It's mostly done for review copies of content where only a handful of reviewers have the content.
Wowfunhappy 5y ago
Watermarking is the kind of DRM I'm 100% okay with. Please, sell me a watermarked but DRM-free video file that I can use with any player on any device. If I share it, you'll know it was me, but otherwise I have complete freedom. Win-win.