Some surprise while "dd-ing" a video DVD...
a.giuliano at iccu.sbn.it
Fri Jan 20 17:24:55 UTC 2006
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?
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
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.
Phillip Susi wrote:
> 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.
>> 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.
Andrea Giuliano, Ph. D.
ICCU - Istituto Centrale per il Catalogo Unico
Viale Castro Pretorio 105, Rome - ITALY
Tel. +39 06 49210403, Fax +39 06 4959302
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