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I reverse-engineered Netflix's 4K restrictions

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Re: I reverse-engineered Netflix's 4K restrictions

#91

Post by direwolf20 »

JCattheATM wrote: post #57
coppsilgold wrote: post #48

Earlier quoted context omitted.

They can trace a torrented 4K piece of content to the device (or private key) that ripped it using A/B watermarking. See AWS offering: (and probably what they use for Prime Video, Netflix has their own) For large-scale per-viewer, implement a content identification strategy that allows you to trace back to specific clients, such as per-user session-based watermarking. With this approach, media is conditioned during t…

To what extent does this watermarking survive transcoding? Would not transcoding multiple times possibly affect it? > They also use a traitor tracing scheme (Tardos codes) such that if multiple pirates get together to try and remove the watermark they will fail, you would need an unreasonably large number of pirates to succeed for some length of time. Why?

The main character holds an apple in her hand. The apple is either pink or bright red depending on the LSB of your user ID. Without comparing several rips, you can't tell this is happening.

Re: I reverse-engineered Netflix's 4K restrictions

#92

Post by direwolf20 »

coppsilgold wrote: post #60
Retr0id wrote: post #59

Earlier quoted context omitted.

Netflix does not encode content per-user, it's all static content on CDNs

A/B watermarking is about static content on CDNs... For every segment in a video there will be two versions. Every user will get a unique sequence of segments served to them.

Isn't it trivial to know all the segments if they are static?

Re: I reverse-engineered Netflix's 4K restrictions

#93

Post by direwolf20 »

coppsilgold wrote: post #66
Retr0id wrote: post #65

Earlier quoted context omitted.

I have indeed inspected the contents of their CDN servers. The URLs have an auth token in them but you can edit the range parameters to grab the whole mp4 in one go without invalidating the auth.

Then this is either an exploit or more likely the mp4 file is virtual. You can find out if you are so inclined by grabbing it from two separate accounts using two separate devices (or keys) and then compare how many of the segments are identical. Also, I assume the file in question is 4K content. Don't know about how they treat other types.

The normal way to do it would be to deliver different byte ranges per user

Re: I reverse-engineered Netflix's 4K restrictions

#94

Post by direwolf20 »

Retr0id wrote: post #52
bigwheels wrote: post #36

Earlier quoted context omitted.

Thank you for sharing the breadcrumb~ How does Netflix detect "suspicious" activity? Does $NFLX allow 4k streaming over GrapheneOS? If so, could you pin a different certificate and do some HTTP proxy traffic manipulation to obfuscate the device (presumably an Android phone) identity or otherwise work around the DRM? I want to understand more about this but unfortunately the reddit thread is bits and pieces scattered…

A DRM system is, abstractly, a black box that contains some initial static key material, which is used to identify+authenticate the device and load in more keys at runtime, typically over some network protocol. The DRM uses those dynamically provisioned keys to decrypt the content. For hardware DRM schemes, the initial key material is typically provisioned during manufacturing. Since the server-side is able to identi…

If it wasn't real, Netflix would leak 4Ks more frequently. We're inferring by a third-order effect.

Re: I reverse-engineered Netflix's 4K restrictions

#95

Post by direwolf20 »

bobdvb wrote: post #81
Retr0id wrote: post #54

Earlier quoted context omitted.

Netflix still saves money when someone watches in a lower resolution.

There's a fine line, reduce quality too far and customer satisfaction drops. Some customers will have a higher tolerance to dropping quality than others, but you've got to draw the line somewhere. So you do studies, you look at the impact of quality changes to customer churn and then you move the line appropriately.

Marketing emphasizing 4K helps reduce this.

Re: I reverse-engineered Netflix's 4K restrictions

#96

Post by direwolf20 »

JoshTriplett wrote: post #38
TacoCommander wrote: post #15

Let's go back to tangible media https://www.rasputinmusic.com https://www.amoeba.com/

I would pay a non-trivial amount for a service that 1) bought a blu-ray on my behalf, 2) ripped it to a file, 3) gave me that file to download, once, and 4) after confirming I had it, shredded the blu-ray. I don't want to copy things and distribute them to others. I want to have one copy that keeps working indefinitely and doesn't go away or fail to follow me across systems.

That's still illegal. A company tried to do that with an array of DVD players.

Re: I reverse-engineered Netflix's 4K restrictions

#97

Post by direwolf20 »

andydevguy wrote: post #79

You can't spoof L1 Widevine.

You could but it'd be much much harder than this.

Everything your computer can do is inspectable with correct application of nitric acid, electron microscopy, and image processing algorithms running on a supercomputer.

You could also try to get hired on the Widevine team or a GPU vendor. Corporate espionage, yay!

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