Re: [libdvdcss-devel] bit perfect copies of CSS DVDs

On 30 Jun, Christoph Anton Mitterer wrote :
> On Tue, 2015-06-30 at 22:16 +0200, Jean-Baptiste Kempf wrote:
> > Right. CSS is both at the file level and at the disk level. You
> > cannot
> > dd directly and have something working.
> > Therefore, when doing copies, you will always remove some part of CSS
> > encryption.
> I see, but even after one has basically "initialised" the device with
> the correct key (by first playing the media via libdvdcss), then the
> UDF still contains files with further CSS encryption, which is why my
> dd dump, when mounted and played afterwards, still shows libdvdcss in
> working, right?

If I understand correctly what you say, yes.

> > > So it seems that in addition to the drive level 
> > > encryption/protection,
> > > which is defeated in (1), there's still another file level 
> > > encryption?
> > > Right?
> > 
> > Well, yes, but I don't know how is that related to your 2).
> Well in (1) "we found out", that there's
> a) encryption at the drive level, which would give me the block level
> errors when the drive isn't sent the key
> b) encryption at the file level, which is still in place after (a) has
> been done
> Right?

Correct.

> So when I dd the disk and mount the UDF image afterwards as loopback
> device, then (a) is gone, but (b) is still present and will need to be
> decrypted.

Correct.

> When I "backup" the disk however with e.g. dvdbackup, then I don't get
> an UDF image but rather normal files VIDEO_TS/*.
> And those are (by name) the same as in the dd'ed UDF image, but the
> binary content of both differs largely.
> 
> So I assumed, that dvdbackup would also do away with (b) and that's why
> the files differ.

Your backup is probably removing the CSS encryption.

> > Are you referring about ARCCOS system?
> Not sure, is there a way to find out whether ARccOS is used?

If your dump make 40GB, or if you see 99 titles.

> hmm strange... any idea where the bug could be? hardware issue?
> libdvdcss?

Sorry, none.

> Just to make things clear:
> The difference is somewhere in the UDF between the two images of the
> same disc.
> But when I loop mount those two dd'ed images and diff the files within
> them - those are the same.
> 
> That's why I thought maybe that's part of CSS, i.e. that the drive
> kinda watermarks the UDF.

Did you read the analysis about DVDCSS?

-- 
Jean-Baptiste Kempf
http://www.jbkempf.com/ - +33 672 704 734
Sent from my Electronic Device
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