5 ms·

No test key required. Inputting the actual key prior to the scheduled slot should cause the projector to show a randomly chosen 30 second segment of the movie,

No test key required. Inputting the actual key prior to the scheduled slot should cause the projector to show a randomly chosen 30 second segment of the movie, with an overlay message at the bottom saying, "Test projection - key valid starting at HH:MM on dd/mm/yy". This should work around 10 times. The overlay should be background-color: #000; opacity: 0.6; color: #fff.

pilif 14y ago
In order to get an accurate prediction whether the presentation is going to work or not, the key must be valid for decrypting the whole movie. If it is, then it can provide no more piracy protection because then you would use it to decrypt the movie independently of the projection system. If the key is only good to decrypt a random part of the movie, then the test says nothing about the success or failure of the key to decrypt the rest of the movie. Tangentially related: what is to stop a technically inclined projectionist to use the key during the time it is valid to decrypt the movie? I would assume that at presentation time, there is enough of decryption key material available to the projection system to cover all of the movie, otherwise a presentation would have to be interrupted as the cinemas internet goes down.
- wtracy 14y ago
  That actually happens: Screenings have been interrupted because the internet connection to the projector gets cut. :-/
  - __david__ 14y ago
    That makes no sense. The KDM is a self contained public-key encrypted message containing the decryption keys. It requires no internet connection to verify and extract the keys, and it certainly doesn't need to do it during the movie. In fact, most projectors are not even connected directly to the internet.
    - xentronium 14y ago
      How do you make sure that system date was not tampered with then?
      - __david__ 14y ago
        I cant remember how that works but I suspect the RTC is in the FIPS can and that it takes effort to set it. They wouldn't go to all that effort to put times in the KDM if someone could just bypass it by setting the system date. It's a pretty well thought out system.
        Thlom 14y ago
        Correct. The DCI says the secure clock only can be adjusted 6 min per year, 20-30 min with a code/package from the manufactorer. If it's adjusted over this limit the mediablock will have to be changed.

pilif 14y ago

In order to get an accurate prediction whether the presentation is going to work or not, the key must be valid for decrypting the whole movie. If it is, then it can provide no more piracy protection because then you would use it to decrypt the movie independently of the projection system. If the key is only good to decrypt a random part of the movie, then the test says nothing about the success or failure of the key to decrypt the rest of the movie. Tangentially related: what is to stop a technically inclined projectionist to use the key during the time it is valid to decrypt the movie? I would assume that at presentation time, there is enough of decryption key material available to the projection system to cover all of the movie, otherwise a presentation would have to be interrupted as the cinemas internet goes down.

wtracy 14y ago
That actually happens: Screenings have been interrupted because the internet connection to the projector gets cut. :-/
- __david__ 14y ago
  That makes no sense. The KDM is a self contained public-key encrypted message containing the decryption keys. It requires no internet connection to verify and extract the keys, and it certainly doesn't need to do it during the movie. In fact, most projectors are not even connected directly to the internet.
  - xentronium 14y ago
    How do you make sure that system date was not tampered with then?
    - __david__ 14y ago
      I cant remember how that works but I suspect the RTC is in the FIPS can and that it takes effort to set it. They wouldn't go to all that effort to put times in the KDM if someone could just bypass it by setting the system date. It's a pretty well thought out system.
      - Thlom 14y ago
        Correct. The DCI says the secure clock only can be adjusted 6 min per year, 20-30 min with a code/package from the manufactorer. If it's adjusted over this limit the mediablock will have to be changed.