4 ms·

Except that in this case, you can't test. The only way to test is to load the movie, load a key and play the movie. No key? No movie, and no test. In addition,

Except that in this case, you can't test. The only way to test is to load the movie, load a key and play the movie. No key? No movie, and no test. In addition, there is no way the distributor will let you have a "test" key. One of those would be manna from heaven for any unsavory projectionist who wanted to make high quality copies from theater prints.

tomsaffell 14y ago
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.
roc 14y ago
Surely they could create test keys that authorize X minutes of playback to test projection. That would make the cam concern moot and address the desire to test the setup prior to show time.
__david__ 14y ago
That's just a software deficiency. There's no reason the software couldn't use the KDM to get the keys and decrypt a frame or 2 (or even a few seconds worth) of the (MXF) film footage as a test, regardless of the time. The encryption isn't numerically tied to clock-times--it's only enforced by the software (which now that I think about it may be enforced by legal contracts somewhere). > One of those would be manna from heaven for any unsavory projectionist who wanted to make high quality copies from theater prints. Not really. The keys and image decryption happen in a tamper-resistant "FIPS can" in the media server and then are re-encrypted and sent across a bus to the projector. Some newer projectors have the FIPS can directly inside so that there are no physically exposed interfaces with anything other than the full-blown AES encrypted frames. Having a KDM means you can play the movie but you can't ever actually get to the data. Fun fact: before DCinema there used to be people who owned tele-cine scanners mounted in the back of flatbed trucks that would go around to theaters and pay unscrupulous employees to borrow the film for a couple hours. They'd have an very nice scan of the movie for pirate DVDs the day the movie came out.

tomsaffell 14y ago

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.

roc 14y ago

Surely they could create test keys that authorize X minutes of playback to test projection. That would make the cam concern moot and address the desire to test the setup prior to show time.

__david__ 14y ago

That's just a software deficiency. There's no reason the software couldn't use the KDM to get the keys and decrypt a frame or 2 (or even a few seconds worth) of the (MXF) film footage as a test, regardless of the time. The encryption isn't numerically tied to clock-times--it's only enforced by the software (which now that I think about it may be enforced by legal contracts somewhere). > One of those would be manna from heaven for any unsavory projectionist who wanted to make high quality copies from theater prints. Not really. The keys and image decryption happen in a tamper-resistant "FIPS can" in the media server and then are re-encrypted and sent across a bus to the projector. Some newer projectors have the FIPS can directly inside so that there are no physically exposed interfaces with anything other than the full-blown AES encrypted frames. Having a KDM means you can play the movie but you can't ever actually get to the data. Fun fact: before DCinema there used to be people who owned tele-cine scanners mounted in the back of flatbed trucks that would go around to theaters and pay unscrupulous employees to borrow the film for a couple hours. They'd have an very nice scan of the movie for pirate DVDs the day the movie came out.