7. What are the copy protection schemes used in DVD ?
What is CSS ?
There are many forms of content protection that DVD technology employs. The two most
popular and well known methods of video copy protection are Macrovision and CSS.
Hollywood movie studios required the DVD specifications to support a comprehensive
copy protection scheme because of the possibility of making an exact digital copy of
the original movies released on DVD. This copy protection method is known as the
Content Scrambling System, or CSS. This is a data encryption and communications
authentication method designed to prevent copying video and audio data directly from
the DVD-Video discs.
The CSS specification was jointly developed by two giant Japanese companies,
Matsushita and Toshiba. In a nutshell, the CSS algorithm scrambles the data in each
DVD sector (a sector can hold 2048 bytes of multiplexed video and audio data) and
hides a 5-byte encryption key in a header area of the scrambled sector. A scrambled
sector size is 2053 bytes. A licensed DVD drive unit can obtain this encryption key
from the scrambled sector to restore the original contents of the sector as seen
before the scrambling process. In theory, it is perfectly possible to figure out the
5-byte encryption key from the scrambled sector data (by using cryptography methods),
but it takes tremendous processor resources to do so. The CSS decryption algorithm
exchanges keys with the drive unit via a process called authentication to retrieve
the required encryption keys that are used to descramble the data from the disc.
DVD players must license the appropriate CSS decrypting algorithm to decrypt the
data before it is decoded and displayed. Manufacturers of equipments used to display
DVD-Video (DVD drives, decoder hardware or software, display adapters, etc.) must
also license CSS. CSS is administered by the DVD
Copy Control Association (DVDCCA)
. In late 1999, the CSS algorithm was defeated
by a Norwegian teenager and posted on the Internet as DeCSS. After many years of
litigation, the Norwegian court system decided that publishing the DeCSS algorithm
is part of the freedom of speech and the author of DeCSS was vindicated. His infamous
work gave birth to DVD software rippers and DeCSS-derivative decrypters. In the
United States, DeCSS-related products are illegal (and even more so with new
interpretations of Digital Millennium Copyright Act), but it is very difficult to
enforce if one just makes a recording for personal or home use.