[libdvdcss-devel] Translation french non-technical description of libdvdcss

Ángel González

2012-04-21 19:14:16 UTC

Post by Crocy .
Hello,
Since I had some time and I both understand English and French, I did
an effort to translate the french non-technical description of
libdvdcss to English. You can find the text at the bottom of this mail
and, if your spambox allows, in attachment. Please keep in mind that
neither English nor French is my mothertongue.
I hope you can use it.

Hi Cristophe,

I've made a few changes to the translation (see inline).
For reference, the original is at
http://www.videolan.org/developers/libdvdcss.txt

Best regards

Post by Crocy .
Non-technical description of libdvdcss (v2.1)
Libdvdcss is a functions library a program can use to explore the
content of a DVD.
1/ The DVD "zones"
All the commercial DVD's and DVD players include "zone
information". Due to this information DVD's and DVD players are
only useable in certain countries because the zone information
from the DVD player has to correspond with the zone information
from the DVD.
2/ The CSS
The CSS (Content Scrambling System) protects the large majority of
the commercial DVD's. Software developers for DVD player buy at
the DVD CCA (DVD Copy Control Association) keys to decrypt the CSS.
At the same time they become the user instructions of the CSS wich
are kept secret.

At the same time they obtain the instructions to use the CSS, which are
kept secret.

Post by Crocy .
Using his key, and while reading the DVD, the software
communicates with the DVD player to get the decryption information.
/3 Copying the DVD
This encryptions don't protect the DVD from copying. It's possible
making a physical copy working perfectly the same (often called
bit-to-bit) when using the right equipment.

These encryptions don't protect the DVD from being copied. Using the
right equipment, it's possible to make a physical copy (often called
bit-to-bit) which works exactly the same as the original one.

Post by Crocy .
And because the medium

Moreover, as the medium

Post by Crocy .
has to be decrypted by the software from the DVD player to show
the content on the screen, this decrypted content is available
during the lecture regardless the used encryption.
4/ The weaknesses of CSS
CSS had been the object of academic studies wich have discovered
how this jamming algorithm works, using retro-analysis.

CSS has been the subject of academic studies which have discovered how
this jamming algorithm works, using reverse engineering.

Post by Crocy .
Later, these studies have shown that the used CSS key are
cryptographically very weak wich has lead to more efficient
decryption algorithms and the discovery of the keys. It's possible
the obtain an exhaustive list on your home computer just in a few
minutes.

Later, these studies have shown that the keys used by CSS are
cryptographically very weak, leading to more efficient decryption
algorithms and the discovery of the keys. It's possible the obtain an
exhaustive list on your home computer just in a few minutes.

Post by Crocy .
5/ How libdvdcss works
This means the list of CSS keys is perfectly known and a sample of
these is distributed with libdvdcss. Libdvdcss has the same
behavior as a DVD player software and uses a key of this sample.
If all the keys from the sample fail, libdvdcss calculates the
rest of the keys and tries them.
It is possible that all this fails, especially when DVD and DVD
player are not in the same zone. As last remedy, libdvdcss
overrides the complete encryption and decrypts the scrambled
stream using the cryptographic weakness of CSS.