Some surprise while "dd-ing" a video DVD...
a.giuliano at iccu.sbn.it
Thu Jan 19 09:05:27 UTC 2006
First of all, thanks for you useful explanation.
> All commercial video DVDs use UDF, not iso9660. The linux kernel has
> supported UDF for several years, which is as long as it has supported DVDs.
I believe in what you say, but actually I can mount a video DVD both as
UDF and ISO9660. As you say, Nautilus and "mount" unlock the DVD before
mount it, that's why I always can mount it.
Yet, I don't understand why dd should not copy a stream of byte from a
device if they represent an encrypted video DVD. I mean, whatever the
bytes represents, dd should dump them. At most, you should get a big,
useless file, but that file should be exactly what was written on the media.
But probably there's something I don't know. You said that mplayer (and
obviously xine, vlc and so on) unlocks the drive, and I guess you mean
"at the hardware level". If it's so, every tools like dd, tar, cpio and
such should fail reading the media.
Am I right?
Another question: is there something one can do before invoking dd to
accomplish the same without using mplayer? I have nothing against
mplayer, it's just curiousity.
> As for packet writing, I'm actually in the process right now of
> improving the udftools package and fixing some bugs in the kernel to get
> support for this fully integrated into ubuntu in a plug and play way.
> See https://wiki.ubuntu.com/PacketCD
>> As far as encryption on dvds go, the dvd itself isn't encrypted, just
>> the .vob files on it. So, if you can't see the VIDEO_TS directory
>> with .vob (mpeg) files in it, then the problem is not with normal dvd
> Actually, the DVD itelf _is_ encrypted, just not the whole thing. The
> sectors that contain the vob files are encrypted at the hardware level,
> which is why dd can not read them. The drive itself performs the
> decryption of those sectors once it has been unlocked. If the data file
> itself were encrypted, then you would still be able to read and copy the
> file even though you could not understand it's contents.
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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