[libdvdcss-devel] CSS authentication changes content returned from drive on some systems only?

[l***@jmbreuer.net]

I've run into an issue while taking care of DVD resume code in XBMC.

A bit of background: XBMC computes a hash over the content of all .IFO
files to use as a Disk Unique ID, to make it possible to identify the
same disk when it is inserted again later and have per-disk persistent
player state / resume bookmarks.

XBMC uses libdvdnav/libdvdread/libdvdcss for DVD access.


I've observed the following: On both of my systems (gentoo on x86_64 and
OpenELEC on x86_64 [different HW]), performing CSS authentication (e.g.
"starting playback") will cause a different hash value to be computed
than before - see https://github.com/xbmc/xbmc/issues/2936

So it seems that performing CSS (my guess: the drive authentication
part) causes different data to be returned from the drive - FOR ME.

The hashes returned "before" and "after" authentication each are stable,
i.e. I always get the same two hashes for a given disc, one before auth,
the other after.


While discussing the issue with upstream, it turns out that another
developer on Windows cannot reproduce the issue - he always gets the
same content/hashes, although the logs show CSS authentication being
performed against his drive as well.
See https://github.com/xbmc/xbmc/pull/2951


Can anyone shed some light on why our systems would behave differently
as they do?


Thanks a lot!


So long,
Joe

[Diego Elio Pettenò]

Just a wild guess honestly, but if your DVD drive is set to region of the
disk you're reading, it will perform the auth in hardware, and libdvdcss
wouldn't be involved.

So I would check with the other developer whether you're using matching or
mismatching drives/discs.

Diego Elio Pettenò — Flameeyes

Post by l***@jmbreuer.net
I've run into an issue while taking care of DVD resume code in XBMC.
A bit of background: XBMC computes a hash over the content of all .IFO
files to use as a Disk Unique ID, to make it possible to identify the same
disk when it is inserted again later and have per-disk persistent player
state / resume bookmarks.
XBMC uses libdvdnav/libdvdread/libdvdcss for DVD access.
I've observed the following: On both of my systems (gentoo on x86_64 and
OpenELEC on x86_64 [different HW]), performing CSS authentication (e.g.
"starting playback") will cause a different hash value to be computed than
before - see https://github.com/xbmc/xbmc/**issues/2936<https://github.com/xbmc/xbmc/issues/2936>
So it seems that performing CSS (my guess: the drive authentication part)
causes different data to be returned from the drive - FOR ME.
The hashes returned "before" and "after" authentication each are stable,
i.e. I always get the same two hashes for a given disc, one before auth,
the other after.
While discussing the issue with upstream, it turns out that another
developer on Windows cannot reproduce the issue - he always gets the same
content/hashes, although the logs show CSS authentication being performed
against his drive as well.
See https://github.com/xbmc/xbmc/**pull/2951<https://github.com/xbmc/xbmc/pull/2951>
Can anyone shed some light on why our systems would behave differently as
they do?
Thanks a lot!
So long,
Joe
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