Cryptography in Home Entertainment (2004) (mathweb.ucsd.edu)

by rvnx 50 comments 82 points
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50 comments

[−] hedora 56d ago
This is a fun rabbit hole to walk down.

You might have noticed that streaming is getting worse (more expensive, less selection, more ads, more fragmentation). For me, they crossed a breaking point, where I decided I'd just find something more convenient.

So, I went down to the local record store, where they have 10,000s of DVDs and Blu Rays in stock; many for $1 (DVD), $2 (BluRay), most under $5-10, and a few gems for $20-30. The prices are for a mix of new and used DVDs; some new DVDs are over-printed, and cost $1.

Problem half-solved. I looked around to figure out how to play these anachronistic shiny disks on my TV, and eventually settled on a USB BluRay RW drive (I guess you can get rewritable BluRays!)

I never figured out how you're supposed to actually use that drive to play movies. Instead, there's DeCSS from the article, then something comparable for BluRay. For the "easy" decryption, you end up downloading per-disk decryption keys for every disk ever printed.

For the more advanced stuff, they have this giant Java Rube Goldberg machine that xors glitches into the video stream. This gets applied at the factory, and then (on some hardware I guess you can purchase?) again via some complicated JVM stack that was originally meant to just render the scene selection menu.

[spoiler alert]

The easiest way to play those BluRays back is to just download the output of the Rube Goldberg machine. At some point the industry realized that scheme was dumb, so there's a finite set of glitch masks. The whole dataset for all BluRays that will ever be produced with this scheme is a few GB.

You might think that when I say "play", I mean "transcode + pirate", but it turns out that's not particularly practical. BluRays are multiple GB, and already compressed with codecs that are competitive with modern ones, so they don't shrink down like DVDs unless you're willing to lose a lot of quality.

So, yes, we have a growing collection of physical media. I target 20-30 movies / $100 when I go to the store. It's grand.

[−] recursivecaveat 56d ago
I used to not be a physical media person. I have found that it makes it a lot easier for me to start and to finish things though. The fact I have to actually get up to swap the disk out if I want a distraction helps focus the attention span haha.
[−] MathMonkeyMan 56d ago
How many GB? I see "bluray rip" mp4 files on torrent index sites, which I assume have been aggressively recompressed, but there are three size tiers in the "1080p" category: 2-3GB, 7-10GB, and 15+GB.
[−] dddgghhbbfblk 56d ago
You want to search for BDMV for full disc images, or for remuxes which are uncompressed video and audio streams, if you want to get a sense for the size on disc. Typical Blu-ray images will be from 20-40ish GB.
[−] miki123211 56d ago
How are today's scene rippers about keeping extra audio tracks and such in these, E.G. audio description?

It used to be quite hard to get an actually actually unmodified disc image.

[−] dddgghhbbfblk 55d ago
Unmodified Blu-ray disc images are the BDMV folders I mentioned. Any BDMV will be unmodified almost all the time though I've very occasionally run into modified ones originating from the Chinese piracy scene that had custom subs added.

A "good" remux is actually the highest quality movie release available, usually, if you don't care about file size. A good remux will combine all the best parts of every possible release into one super-file. For one movie, you could have the best video quality be on a French UHD Blu-ray, the best audio quality from a different source, subtitles aggregated from various international releases and streaming platforms (and filtered/deduped for quality), chapter titles taken from an old DVD, and all available commentary tracks collected. Rarely you might even see a hybrid release where multiple streams are spliced together to fix some problem or another in one of them. You can look for releases by the CINEPHILES p2p group for gold standard examples, they get distributed fairly widely so you can probably find some.

To answer what you asked about extra audio tracks specifically (outside of full disc images)--usually non-English dubs are considered bloat and aren't distributed. Commentary tracks are kept. Audio description is a mixed bag, good groups will keep it.

[−] progbits 56d ago
On private trackers where people care about that stuff it's easier. The NFO usually has a pretty comprehensive description of the contents and all the tracks etc so you can decide which version you want before downloading.
[−] ThrowawayTestr 56d ago
It really depends on your hard drive space and your tolerance for compression. Two hours of decently compressed video is a few gigs, but if you want 10-bit HDR with 5.1 audio, then choose the 15 gig torrent.
[−] hedora 54d ago
If I wanted it to be a few gigs, then I'd have bought the $2 DVD, and not splurged on the $5 bluray!
[−] gsich 56d ago
codec? x264 and 1080p is in the ~8GB range for a 120min movie. Depending on audio might be more.
[−] hedora 54d ago
https://www.sony.com/electronics/support/articles/00029663

VC-1, H.264 (MPEG-4 AVC)

Also, the studio paid a professional to peep at all the inter-frame pixels and turn the knobs right when they encoded the bluray. I might be able to get a perceptually lossless rip that's 25-50% smaller than the original, but it's just not worth my time.

[−] stevekemp 56d ago
Same story here, I can be used films on DVD for €1 at many charity shops. Boxed sets of TV shows are €2-5 depending on size/popularity.

The only downside is that I've noticed that the used DVD sections are definitely getting smaller. I guess fewer people are donating their collections these days.

I've bought a couple of DVD sets from Amazon, used, but the prices there aren't so competitive. Still it's nice to have physical media, with real/original soundtracks.

[−] 1317 56d ago

> The easiest way to play those BluRays back

buy a bd player? i don't know why you would settle on a usb rw drive when you could just have a box that plugs in via HDMI and works

[−] ThrowawayTestr 56d ago
I just torrent everything. It's equally as illegal.
[−] flomo 56d ago
Worth noting the industry knew that CSS was a lousy scheme. Originally, Disney and others were boycotting DVD because of it. That lead to DIVX (the disk not the codec).

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

Some people were opposed to DIVX's 'phone home' PPV option, but the bigger issue was it seemed like a nasty format war was brewing. Then DIVX flopped quickly. Instead, the MPAA got the US Congress to "patch" CSS by passing a law.

Apple had an advertising campaign that you could "Rip. Mix. Burn." your CDs with a Mac. Obviously nerds could rip DVDs, but nobody ever could productize it like that.

[−] flomo 56d ago

> The original reason behind the DVD scrambling system "needing" to be cracked was the lack of software DVD players for the Linux operating system.

Also, this is a false history, and more of an ex-post-facto justification.

The original DeCSS was a VisualBasic program written by some W1nd0z h8X0r teenager. Not for any greater cause, just because they could.

[−] charcircuit 56d ago

>He hadn't pirated anything, only made a program to view his DVDs in Linux.

He released a tool for circumventing a protection measure. While already illegal to do in America, it wasn't made illegal in Norway until less than 2 years later.

[−] janci 56d ago
How was CSS supposed to protect against copying the encrypted data? We should not need to decrypt the video to duplicate the disc.
[−] y7 56d ago
The link to cryptanalysis details is no longer working. Here's an alternative: https://www.cs.cmu.edu/~dst/DeCSS/FrankStevenson/analysis.ht...
[−] badcarbine 55d ago
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