Why aren't known-plaintext attacks against digital media trivial ?
John Case
case at sdf.lonestar.org
Thu Oct 8 05:30:14 PDT 2009
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 ? :)
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