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

[Shawn K. Quinn]

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.

-- 
Shawn K. Quinn <skquinn at speakeasy.net>