Play encrypted DVD

[CONTEXT]
Playing encrypted DVD, sometimes you can recieved a error message like
 libdvdread: Encrypted DVD support unavailable.

[WHEN] 
You want to play encrypted DVDs with Linux.

[HOW]
As root
Edit your /etc/apt/source.list, adding this line

 deb http://www.deb-multimedia.org wheezy main non-free

The first package to install is deb-multimedia-keyring.

# apt-get install deb-multimedia-keyring
Install the library  libdvdcss2
# apt-get install libdvdcss2

After this steps, your dvd's player will be able to play DVD

[SOURCE]
http://www.cyberciti.biz/faq/debian-linux-squeeze-installing-libdvdcss2-command/ 
http://www.deb-multimedia.org/ 

[OTHERS ALTERNATIVES]
http://theos.in/desktop-linux/linux-playing-encrypted-dvd/
http://www.cyberciti.biz/faq/howto-ubuntu-linux-playback-dvd/