Why aren't known-plaintext attacks against digital media trivial ?

[John Case]

On Thu, 8 Oct 2009, Shawn K. Quinn wrote:

> On Thu, 2009-10-08 at 05:39 +0000, John Case wrote:
>> Let's say I am authoring a video clip for blu-ray.  I have a scene
>> transition that goes to solid black.  Let's further say that the tool I am
>> using allows me to insert such "screens" and I define them with hex color
>> values ... so I simply say "fill screen with #000000 for 2 seconds".
>>
>> Which essentially turns into a display resulting in 1920x1080 pixels of
>> that hex code.  For 30-60 frames per second.
>>
>> Why aren't events like this huge sources of known-plaintext ?
>
> They are. This was how the 40-bit cipher used for DVD's CSS was cracked.
> With modern 128-bit ciphers it's a lot harder to crack even with known
> plaintext; the MPAA learned their lesson.


Thanks.  Are there authoring constraints as well ?  There is some cost 
involved in authoring a blu-ray disc, but they're not astronomical.

Presumably there is some kind of mechanism to stop someone from authoring 
and releasing a copy-protected disc with 10 minutes each of black, white, 
and all the primary colors ?   :)