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

[Andrea Giuliano]

Phillip Susi wrote:
> Andrea Giuliano wrote:
> 
>> 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.
>>
> 
> What do you mean you can mount it as iso9660?  If the disk is UDF you 
> certainly can't mount it as iso9660.  Usually your /etc/fstab will 
> specify udf,iso9660, which means EITHER filesystem is acceptable, and 
> both will be tried until the correct one is found.

I mounted "Shrek" right now, without any options, and it was mounted as 
ISO9660. I umounted and remounted it as UDF ("-t udf"), and now it is 
mounted as UDF. Here are "ll /mnt" in both cases, first ISO9660, then UDF:

total 745
dr-xr-xr-x  1 root root   2048 2001-09-14 01:34 audio_ts/
-r-xr-xr-x  1 root root     73 2001-09-06 14:28 autorun.inf*
dr-xr-xr-x  1 root root   2048 2001-09-06 14:27 common/
-r-xr-xr-x  1 root root    173 2001-09-06 14:28 disc.id*
-r-xr-xr-x  1 root root 734208 2001-09-06 14:28 install.exe*
dr-xr-xr-x  1 root root   2048 2001-09-06 14:27 mepatch/
-r-xr-xr-x  1 root root  14914 2001-09-06 14:28 readme.txt*
dr-xr-xr-x  1 root root   4096 2001-09-14 02:56 video_ts/
dr-xr-xr-x  1 root root   2048 2001-09-06 14:28 win/

total 750
dr-xr-xr-x  2 4294967295 4294967295     40 2001-09-14 01:34 AUDIO_TS/
-r--r--r--  1 4294967295 4294967295     73 2001-09-06 14:28 AUTORUN.INF
dr-xr-xr-x  4 4294967295 4294967295    232 2001-09-06 14:27 common/
-r--r--r--  1 4294967295 4294967295    173 2001-09-06 14:28 disc.id
-r--r--r--  1 4294967295 4294967295 734208 2001-09-06 14:28 install.exe
dr-xr-xr-x  4 4294967295 4294967295    236 2001-09-06 14:27 MEPatch/
-r--r--r--  1 4294967295 4294967295  14914 2001-09-06 14:28 README.TXT
dr-xr-xr-x  2 4294967295 4294967295   2068 2001-09-14 02:56 VIDEO_TS/

Please note that I can't say how this happened, just show you what I did 
and the result. I had the same result with all other video DVDs I tried. 
  Most of them just have the canonical dirs "audio_ts" and "video_ts".

> 
>> 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.
>>
> 
> Because the encryption is done at the hardware level, the drive will 
> refuse to read those sectors unless it can correctly decrypt them.  The 
> firmware in the drive will return an error rather than the encrypted data.

Clearly, dd is to simple to unlock the drive, but see below...

> 
> I'm sure there is some other way to unlock the disk, but I don't know of 
> one.  It's easy enough though to just fire up mplayer for a second ;)
> 
I agree!

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