Some surprise while "dd-ing" a video DVD...

[Phillip Susi]

Andrea Giuliano wrote:
> I must agree with Noah: just VOB files are encrypted, and not at the 
> hardware level. That doesn't explain the strange dd's behaviour, but 
> explains what mplayer does, described in the following two points:
> 

Only the parts of the disc that contain the vob files are encrypted, but 
it is most definitely done at the hardware level.  The player itself 
must decrypt those sectors and it can not ( because it has not been 
unlocked ) it fails requests to read them.  This is why dd can not read 
the disc.

<snip>

> 
> This, to me, means that the disk is not encrypted, so that you can mount 
> it, "cat" it, "dd" it and so on. But if you want to watch the movie, you 
> need to decrypt every single VOB file. Nothing makes me think of a 
> hardware level encryption.
> 

Again, only the sectors that contain the vob file are encrypted, which 
is why you can mount the disc and see the filesystem directory 
structure.  This is also why dd manages to read the first couple of 
sectors, then fails when it hits the ones containing the vob files.

If only the file data itself were encrypted, then you would easily be 
able to copy the disc, and that's exactly what the MPAA wants to prevent 
you from doing.

> I'd really appreciate your interpretation: I definitely am not a 
> technician, as you instead maybe are.
> 
> Best regards.
>