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

[Andrea Giuliano]

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.

Best regards.

> 
> 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
>> encryption.
>>
> 
> 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
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