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.

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.

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.

And because the medium 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. 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.

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.

Regards,

Christopher