[MPlayer-users] Re: how does mplayer circumvent region protected (RPC-2) DVD drives?

[Arpi]

Hi,

> Thing is that there are several phases of authentication. If I remember
> correctly:
> 
> 1. Player authenticates with player key, gets disc key.
> 2. Player unlocks ``hidden sectors'' with disc key. Hidden sectors
> contain title keys for each title on DVD, and sometimes several sectors
> of the VOB-s themselves.
> 3. Player requests title key.
> 4. Read, decrypt using title key and play.
> 
> For the reason beyond my knowledge region checks in RPC2 drives are
> performed only in stage 3. mpdvdkit avoids them by not requesting the
> key at all, it cracks the key using ,,known plaintext attack'' on VOB
> contents.

not completely true.
libdvdcss 1.x (used in mpdvdkit too - note again it isn't our work, mpdvdkit
is libdvdcss+livdvdread+some patches together) first try to do the 'legal
method', what you described (get disc key, then decrypt title key with disc
key). but, if it fails, then it has 2 other methods:
2. crack the title key by knowing the decrypted VOB content (vob has very
strict file format, so it can be predicted well). probably it's called
,,known plaintext attack'', i'm not a crypto expert. slow, and sometimes
doesn't work.
3. crack the disc key, by building a 64MB (16M 32bit entries) hash table.
 -> very very slow, but afaik always work.

note, that libmpdvdkit contains a patch (refused by dvdcss developers) which
saves decrypted keys to file, so they don't have to be cracked next time.

> PS. Maybe it should go to TFM after all...
yes, i asked doc ppl then, but it is still not added.

> PPS. I suspect that the reason why those checks are performed in stage
> 3 only is that DVD standard may allow for DVD discs containing several
> titles with different region restrictions.
i'm not sure it's done in stage 3.
for region1 disc my region2 drive fails to read the disc key.


A'rpi / Astral & ESP-team

--
Developer of MPlayer, the Movie Player for Linux - http://www.MPlayerHQ.hu