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

John Case case at sdf.lonestar.org
Wed Oct 7 22:39:55 PDT 2009

(full disclosure: I am not a video/media person at all - I have only a 
loose understanding of their job and workflow)

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 ?

Presumably this could occur in any digital medium - programmatic silence 
in a digital audio clip, or screens/fillers/pages like the one described 
above in both satellite and cable TV broadcasts (although the blu-ray 
example is easier to deal with, since you're not dealing with 

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