How encryption for Cinema Movies works

https://serverless.industries/2024/05/31/digital-cinema.en.html

by perryflynn • 1 year ago

230 120 1 year ago

Fascinating read and I think an accessible presentation of a lot of the concepts / framework and mechanics of this type of system.

john01dav• 1 year ago

Even with all of this onerous encryption and DRM, it's not hard to find pirated copies of movies. It makes me think that the sacrifice in ownership rights for the theaters over their equipment isn't worth it.

ajsnigrutin2• 1 year ago

Yep, and those pirated copies are DRM free, work everywhere, no HDCP and other crap, no internet connection needed, so they're "better" in that way too (not just price-wise).

eastbound• 1 year ago

Totally possible that watermark identifies cinemas and showtimes uniquely, and that pirates are due for a lifetime of prosecution. Or that studios will shut down some cinemas, until it stops.

For 15 years you let paid options progress. Then fewer people pirate, then you catch the rest. At the beginning you don’t see it putting its clamps; then suddenly you don’t find piracy anywhere.

gruez• 1 year ago

Most pirated copies aren't from theatrical releases; they mostly come out when the titles are available on streaming/blu-ray. DRM might be a failure in other fields, but it's working pretty well in this particular case.

johnisgood• 1 year ago

I think the question remains, is it still worth it given these holes?

perryflynn6• 1 year ago

It also contains watermarks. So theatres which failed to prevent recording will run into serious issues. See https://dcpomatic.com/forum/viewtopic.php?t=2372

thr0w4• 1 year ago

NexGuard is a wild product.

coppsilgold• 1 year ago

If the software to watermark is widely available (as it appears to be) then an adversary has all they need to corrupt any existing watermark.

These steganographic watermarks depend on no knowledge of the process. If the method is particularly ingenious (one of the inputs is centrally stored entropy which the extractor references by trialing them all) then knowledge of the process alone may not be sufficient to obtain a high quality result (as too much corruption may be required) but could be used to inform the next step:

If you obtain two or more copies of the decrypted content you will be able to diff them and work out what you need to corrupt even without knowledge of the watermarking process. This probably won't work with pirated CAM's or take quite an effort to find the signal in the noise.

Edit: After some more research it looks like they don't actually watermark the distributed data (the movie sent to cinemas). The projector inserts its unique watermark during playback. There may be other secret watermarks put in by distributors not mentioned anywhere.

codemiscreant• 1 year ago

There is essentially zero piracy from these digital cinema releases. The pirate copies are generally from once it starts digitally streaming on one of the services including PPV, and when pirate copies exist earlier it is almost always someone with a camera in a theatre making a terrible quality screener.

Piracy is inevitable, but in this case their model is much more robust that I would have predicted.

tptacek• 1 year ago

Most importantly, the industry concerns itself primarily with the new-release window; that high fidelity copies will eventually be widely available doesn't break the model.

kelnos3• 1 year ago

Not sure of the GP's core message there, but I think this is kinda the point: even with all this onerous encryption on the cinema releases, high-quality pirated copies still very quickly make it out.

So basically they have this very secure scheme for getting movies to theaters, but everything else is full of holes. Makes you wonder if all the effort and cost to secure the theater distribution chain is worth it. If you're going to allow playback on devices in "adversarial" hands (streaming, home physical media playback), it's going to be incredibly difficult to restrict copying. Tightening up the one instance where the hardware and people operating it have less incentive to pirate (and more incentive to not pirate, given the risk to their theater business) seems like wasted effort.

Certainly this does make the case of a theater-only-first release nearly impossible to pirate. But there aren't quite as many of those anymore, and all this DRM must be expensive, both in the hardware/software, and in the logistics. I guess they've found it's worth it, but... oof.

dvngnt_• 1 year ago

Back in my day the first releases were cam rips sold on dvds for $3-5 per movie. quality wasn't great but the audio could be ripped from the devices for hearing impaired https://en.wikipedia.org/wiki/Telesync

quality varied but was good enough in mid 00's probably better

sandworm101• 1 year ago

There is zero piracy from projectors because there are a multitude of easier places to rip from. But close those doors, limit to only theatrical releases, and we will again see content pulled from projectors and underpaid projectionists.

The only way to prevent piracy, to actually prevent copying, is to keep content in a dark vault well away from public view.

teeray• 1 year ago

it is almost always someone with a camera in a theatre making a terrible quality screener.

Could an insider do a more sophisticated telecine capture with more fidelity?

Aurornis4• 1 year ago

Pirated copies of theatrical releases at the time of release are much more rare, though.

The value of protecting releases is extremely high in the narrow window of finalizing production and getting it into theaters or online launch platforms.

If there was no DRM and watermarking then these would be pirated constantly before release.

anal_reactor2• 1 year ago

Most people are completely fine watching a 720p x264 1GB version half a year after release. Sure, there are some purists who want as good image quality as possible as soon as possible, but that's a tiny minority. I think the actual motivation is that cinemas are becoming less and less relevant in the age of streaming, so they're doing anything they can to protect the little revenue they have, because the only way cinema can make money is to hype a movie to the moon, and then have it shown exclusively in cinemas for some period of time. But with streaming services investing in their own movies, the days of this distribution model are numbered. Having a cinema in 2025 is like having an internet cafe in 2010.

yladiz• 1 year ago

This really downplays the cinema experience. Yes, many people are fine watching a movie at home while doing something else (the current Netflix model of filmmaking is precipitated on this), and others are fine to watch at home in general, but few people would truly say that their setup is close to what you get in a cinema. The screen is much bigger, the image quality is higher, and the sound system is much better as well, compared to anything short of an actual home cinema setup. It’s not the only reason of course, but it’s one of a few reasons cinemas still sell out for big films like Dune 2, and why people will go out of their way to go watch it in the cinema.

Streaming will never fully replace cinemas, even if it dramatically impacts their operating mode, and to argue otherwise is naive.

fmajid2• 1 year ago

Quite often it's industry insiders themselves who release rips from the Blu-Ray screener disks sent for Academy Awards consideration.

ddtaylor• 1 year ago

How are groups getting the high quality digital dumps of some movies then?

pain_perdu• 1 year ago

I don't think new theatre releases are generally getting leak in digital formats anymore until they hit streaming which can sometimes be as soon as weeks or couple months after original release. Obviously 'tele-syncs' (cameras capturing the film) still exist but that wasn't your question. The one exception to this can be oscar movie season when studios release films via a special Apple TV app and that be be slightly less secure (though still water-marked).

I would ask you to support your claim of 'high quality digital dumps' by citing one that has come out in the last couple years. See https://predb.net/

lurk2• 1 year ago

A telesync (TS) is a bootleg recording of a film recorded in a movie theater, often (although not always) filmed using a professional camera on a tripod in the projection booth. The audio of a TS is captured with a direct connection to the sound source (often an FM microbroadcast provided for the hearing-impaired, or from a drive-in theater). If a direct connection from the sound source is not possible, sometimes the bootlegger will tape or conceal wireless microphones close to the speakers, as it is better than a mic on the camera. A TS can be considered a higher quality type of cam, that has the potential of better-quality audio and video.

https://en.wikipedia.org/wiki/Telesync

kmeisthax3• 1 year ago

Hollywood is stupid and eroded its own economic advantage by putting everything on streaming. This was already known, but it also makes antipiracy operations much, much harder.

Ripping a stream is always going to be easier than getting any unprotected video footage out of a movie theater. The stream is in your own home, you own and can tamper with all the equipment involved in playing it, and the economics of CDNs prevent robust traitor-tracing schemes[0] that could be used to hunt you down.

In contrast, movie theaters are public locations, so every one of them is a known entity. The entire supply chain for movie projection is controlled. And that makes traitor-tracing a lot easier. All the hackers pointing out that DRM is fundamentally breakable are ignoring the fact that that only matters iff you're anonymous and untraceable. Otherwise, they won't bother making the DRM stronger, they'll just arrest people until the movies stop leaking.

It's the XKCD laptop wrench story[1] in reverse. The crypto nerd imagines DRM to be easily broken trash, but the reality is that the security of the DRM is in the $5 wrench, not the math.

Let's play contrast-and-compare. If you want to leak a stream, you need:

- A streaming account

- Knowhow or software to decrypt the data stream as it's downloaded and played, or,

- Knowhow to modify a TV so that you can capture the unencrypted video and audio streams inside the TV

The last one isn't done because it's a pain in the ass and the TV scene prefers bit-perfect rips over re-encoded captures. But at some point in the TV, you have to decrypt the video; LCD panels do not natively accept encrypted signals. And that is something you can build hardware to capture.

Now let's try leaking a movie. There's a few avenues of attack, roughly corresponding to the traditional movie scene release categories:

- You can go to the theater and point a camera at the screen. They actually check for this now, in pretty much any western country you'll get kicked out or arrested for camming a movie. If you don't get caught, they can still narrow you down to a location in the room via your shooting angle, and possibly determine what theater you were at with line frequency hum. That's enough information to narrow down the guy leaking the movie to a handful of customers. Do this enough times and you create a unique fingerprint to catch yourself with.

- You can get a job as a projectionist and run the movie projector into another camera directly. That kind of machine is called a telecine, and it used to be one of the higher quality ways to get leaked movies back when they were on film. This is specifically the scenario that all the DRM in the projector is designed to stop. If you do anything to change the light path of the projector, it locks up until the manager comes in and types a password to authorize the change.

- You could bribe the manager or owner to telecine the movie for you. Problem is, the number of people who actually have the password that unlocks the projector is really small[2] and traceable. If a telecine leak is traced back to their theater, someone's getting fired at a minimum, jailed in the worst case.

- You could break the DCI scheme itself; but you still need to source the files and keys to decrypt the movies. This is the crypto nerd's imaginary scenario. Even then, the files could themselves have steganographically injected information identifying the theater who got that master copy, which you can't strip out merely by having the encryption keys. Again, nobody is giving you those files unless they're too stupid to understand the implications (unlikely) or they have faith that you can strip out the stegotext.

It's just way easier to rip a stream than a movie in a theater. And when Hollywood moved to streaming they also made it a lot easier to leak movies.

[0] To be clear, traitor-tracing each stream would require a unique encode per account to inject the stegotext; that's computationally unfeasible. Doing one encode per movie theater would still be a struggle, but less so by three orders of magnitude.

[1] https://xkcd.com/538/

[2] This is also why the 3D era of film made movies way too fucking dark.

mysteria2• 1 year ago

To be clear, traitor-tracing each stream would require a unique encode per account to inject the stegotext; that's computationally unfeasible. Doing one encode per movie theater would still be a struggle, but less so by three orders of magnitude.

If the movie is streamed in chunks, only certain short segments would need to be reencoded to add watermark data. Alternatively it might be possible to splice in a short segment with the watermark between keyframes of the preencoded film.

Finally all of this could be done on the audio side which is much less computationally intensive compared to video.

thaumasiotes• 1 year ago

Problem is, the number of people who actually have the password that unlocks the projector is really small[2]
[2] This is also why the 3D era of film made movies way too fucking dark.

What is the relationship between these two things?

lern_too_spel• 1 year ago

Hollywood is stupid and eroded its own economic advantage by putting everything on streaming.

If moving to streaming made them less money, they wouldn't have done it.

dist-epoch2• 1 year ago

Hollywood is stupid and eroded its own economic advantage by putting everything on streaming

You are making a big assumption that they had a choice, that if a movie was not put on streaming, the consumer would go to the cinema to watch it.

But many consumers don't, if the movie is not streaming, they just don't watch it at all.

stepupmakeup• 1 year ago

Screener leaks or insider (outsourced VFX for example) leaks

Animats2• 1 year ago

JPEG 2000 for each frame? I wonder what they use for decompression. JPEG 2000 decompressors are really slow. Most couldn't keep up with frame rate without GPU support.

userbinator2• 1 year ago

Dedicated hardware, not even regular GPUs. JPEG2000 decompression has a rather complex entropy decoding part which is not easily parallisable.

fulafel• 1 year ago

Only on the intraframe level - Frames are independent so overall it's "embarrassingly parallel".

Aurornis4• 1 year ago

The parallel part would come from batch decoding upcoming frames across multiple cores and buffering the result.

4K at 90fps decoding is easy for commercial decoders with a consumer GPU. The dedicated hardware solutions are out there but they’re not the only way to do it any more.

perryflynn6• 1 year ago

The frames are sent encrypted into the projector. The projector has special hardware for decrypt and decode.

andreashaerter• 1 year ago

I also recommend an insightful talk by the author of the article, delivered at a Chaos Computer Club (CCC) event (GPN, Gulaschprogrammiernacht) on this topic. Unfortunately, it's only available in German, but it's definitely worth watching: https://media.ccc.de/v/gpn22-382-kein-kinoerlebnis-ohne-korr...

„No cinema experience without correct certificate management... A look behind the scenes of a cinema with a digital projector system, how distributors deliver films to cinemas with end-to-end encryption, and how films are protected from piracy. In addition to an overview of projector technology, the presentation will demonstrate the file format and manual decryption of film data.“

Edit: I just realized that the author of the article also delivered the recorded talk, adapted my comment.

jeffbee2• 1 year ago

It's remarkable that they do all this in the context of box office revenues cratering. In 2024 American theaters has less gross ticket sales than they did in 1982, in constant dollars. The whole thing of movie theaters is just over.

tverbeure3• 1 year ago

Why does that context matter? It's not as if the use of DRM for movie theater distribution influences whether or not somebody goes to see a movie.

jeffbee2• 1 year ago

No, the other direction. Clearly the problem is that nobody wants their product, not that everyone wants to steal it.

KaiserPro3• 1 year ago

Encrypted DCPs have been around since when DVDs were still a revenue generator.

dherls• 1 year ago

I'm confused why it's encrypted as a JPEG image per frame instead of one AES encrypted video file. Since the same AES key is used for each frame it wouldn't add any additional security imo

Aurornis4• 1 year ago

I think JPEG 2000 is simply the chosen format for distribution of the video, not for security.

JPEG 2000 has some interesting properties for very high quality video storage and transport where bandwidth is not a concern. The traditional encoded video formats we know are less preferred at this scale.

JPEG 2000 is resource intensive, though. The decoding hardware is probably either GPU based or using an FPGA implantation from one of the providers who makes hardware for this.

userbinator2• 1 year ago

It's definitely dedicated hardware JPEG2000 decoding.

KaiserPro3• 1 year ago

DCPs were designed to be jpeg200 streams with a bunch of audio streams as well.

The idea was that they wanted up to 16bit colour (per channel) lossless imagery. The encryption was (or so I recall) was an extra feature.

perryflynn6• 1 year ago

One movie can be 200G to 1TB large. The chunked encryption allows it to seek the movie without decrypting from the beginning.

01HNNWZ0MV43FF• 1 year ago

But any computer with full disk encryption also has seekable encryption

Biganon• 1 year ago

As per asdcplib's author themselves in another clmment:

Frame-by-frame encipherment, rather than whole stream, better supports random access and the famous tobacco intermissions popular in the EU.

shmerl• 1 year ago

"Standards that have to be purchased". Someone is just trying to fleece the participants. That's what whole DRM is about most of the time.

tverbeure3• 1 year ago

Standards are often cheap. Many tech companies have a subscription to all IEEE papers and standards. The incremental cost of downloading one standard more is in the noise. But even if you don't have a subscription, the price for, say, the 802.11n standard is only $381.

KaiserPro3• 1 year ago

Packaging DCPs used to be a massive faff. (it might still be one)

Basically they are a tar[1] of images with a bunch of audio streams for different speaker configurations. depending on the quality settings, they can be encoded for higher colour space (ie 16 bit log per channel)

Even with lossless jpeg2000, these packages can be huge.

But, back in 2011, the biggest problem was encoding jpeg2000 required hardware to get anything near realtime performance. (I also think there were dedicated DCP packaging machines, but I never actually saw one.)

One of my colleagues decided the best way to ship the finalised movie was to open up an NFS port on sohonet and let the technicolor hook the DCP packager directly.

it worked, but our CTO diplomatically asked them to stop.

[1] not actually but conceptually similar

jackjeff2• 1 year ago

The video stream is encoded as one single JPEG2000 picture per frame. Each frame is encrypted with the same static AES key.

Is this not a problem? It’s not a good idea to reuse the same key to encrypt very similar files. Similar to ECB. See the famous penguin https://words.filippo.io/the-ecb-penguin/

I’m surprised they don’t use something like XTS commonly used for disk encryption. It derives a unique key for each block/frame and allow you to access each individual blocks/frames non sequentially.

perryflynn6• 1 year ago

No. They use a unique IV for each frame:

Every Frame is using a unique IV (Initialization Vector), which ensures that the AES Block Cipher generates always different cipher texts and makes brute force harder. This works similar to a Password Salt.

jackjeff2• 1 year ago

Oh thanks. I missed that. I guess that works pretty well too!

NoMoreNicksLeft• 1 year ago

Encrypted DCPs use Forensic Watermarks which contain the serial number of the projection system. So if a recorded copy of a movie appears online, the theatre will have to answer serious questions and may never get movies again.

Is this not as simple as dumping the same movie from two different projectors, diffing the output, then obfuscating the watermark?

TheDcoder• 1 year ago

To do that you need to figure out what parts are noise (watermark), simply diffing them would just give you a different noise pattern which can still be analyzed depending on how the watermark is encoded.

asdcplib• 1 year ago

Hi, asdcplib author here (mentioned in the article.) Excellent writeup of DCP and related tech. FYI the colorspace of an SDR DCP MXF file is X'Y'Z' with gamma 2.6 (see SMPTE 428-1.) Other MXF formats (i.e., not cinema) use a wide variety of colorspaces. Despite the huge range of XYZ, DCP image files are usually constrained to code values that fall within P3 (again, SDR.) The HDR applications are more interesting.

Upon reading the comments: • DCP is a B2B format. DCP usage is licensed by contract, not EULA. Please keep these important differences in mind when commenting on DRM. • Decrypt, decode, color processing, watermark occurs in FPGA. If you think that sounds hard, remember that all of this tech was originally deployed 20 years ago. Moore's law has made our lives much easier since! • Frame-by-frame encipherment, rather than whole stream, better supports random access and the famous tobacco intermissions popular in the EU.

hbcondo714• 1 year ago

31. May 2024

I’m trying to understand the timeline here; the article was originally written last year and the latest spec is also from 2024 but the article has a link to this HN thread created yesterday?

baud1472582• 1 year ago

Maybe the author saw a bunch of hits coming from HN and edited his post to add the link to the discussion? It doesn't seem as if the author themselves posted their article.

perryflynn6• 1 year ago

Yes, I added some notes/improvements while the discussion was happening here.

Changelog: https://github.com/perryflynn/serverless.industries/commits/...

vitplister• 1 year ago

Maybe someone with more knowledge could comment on what happened here: https://wikileaks.org/sony/docs/05/docs/Digital%20Cinema/Dig...

perryflynn6• 1 year ago

Well, the DCI system relies on trusted (TPM-ish) hardware. One server vendor has used insecure certificates. So if a AES key for a movie is encrypted / shipped for such insecure certificate the AES key for the movie can be decrypted outside of the actual projector hardware.

This is one reason why they use Device lists, if such a issue becomes public, they will just block this specific projector or the whole product line for future movie releases and the leak is contained.

Also only movies which got assigned to that projection system are affected. So the damage is low/medium.

How encryption for Cinema Movies works

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