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

[Phillip Susi]

Andrea Giuliano wrote:
> Okay, I think I almost got it, now: since some sectors can only be 
> decrypted at hardware level, an attempt to read them with the 
> appropriate system calls would give an I/O error, right?
> 

Correct.

> This explains also the following: I had right here another system with a 
> different drive, but the same OS (Breezy), and I don't need libdvdcss to 
> copy the same video DVDs with dd. I can remove libdvdcss it completely, 
> eject and reload the disc, or even another one, and dd works fine till 
> the end of the disc. I guess this means that this particular drive is 
> able to give the OS access to encrypted sectors without the need of 
> libdvdcss, right?
> 

You might need to power cycle the machine to reset the drive and make it 
'forget' the decryption key.  Assuming the disc is encrypted ( which it 
is if it's a commercial movie dvd ) and that you don't have libdvdcss 
installed or something else that can unlock the drive, then dd will fail 
to read most of the sectors on the disk, which was the original problem 
that started this thread.

> But please, lead me to some good documentation, I don't want to bother 
> the other users on the list with this issue any more, nor you yourself, 
> except you explicitly tell me you don't mind to carry on the discussion 
> a bit between us.
> 


The wikipedia is a good palce to start:

http://en.wikipedia.org/wiki/Content-scrambling_system