Japan’s Broadcast Protection Solution
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Satellite digital TV in Japan started early with the launch of digital standard definition television broadcasts in 1996. Japanese broadcasters then began digital terrestrial television broadcasting (DTTB) in major metropolitan areas in December 2003. Since then, the Japanese government has indicated that all analog TV will be discontinued in 2011 after the achievement of national coverage of DTTB scheduled for the same year.
 
In their conversion to digital, Japan’s broadcasters have adopted the Integrated Services Digital Broadcasting (ISDB) standard as the digital TV and digital radio format. The fact that ISDB supports Digital Rights Management (DRM) technology which enables content protection was a key factor behind its adoption. Today, ISDB encompasses a number of standards that include ISDB-S (satellite), ISDB-T (terrestrial), ISDB-C (cable) and 2.6GHz band mobile broadcasting.

Japan’s content protection solution

With the broadcast of images or sounds becoming digital, repeated copying of a broadcast does not cause deterioration in quality. As a result, DVD or hard disk recorders can easily create faithful duplications of content in large quantities allowing a significant amount of pirated content to enter the market. The ease with which copyright could be violated in such a scenario could make movie and music copyright holders reluctant to provide their works on digital media and prompt actors and singers to refuse to appear or perform on TV or radio. As a result of this danger, duplication controls through the encryption of the broadcast signal was introduced in Japan in April 2004 to secure broadcast copyrights.

In Japan, broadcasters encrypt content before its transmission for purposes of copy protection, regional control of viewing, and pay TV charging. Encrypted content is transmitted to a user’s set-top box which then decrypts the content through the use of “keys” stored in a B-CAS card.

For content protection purposes, this encryption solution supports three modes of duplication control: “copy once”, “copy free” and “copy never”. In “copy-free” mode a TV program can be permanently stored and copied without technical restriction onto digital media devices such as Digital VHS (D-VHS), DVD or hard disc recorders. In “copy never” mode a TV program can only be time shifted and cannot be permanently stored on a digital media device.

In Japan, every digital TV broadcast, including free-to-air, is encrypted in “copy-once” mode. In practice, this allows users to record a TV program to a copy-protected digital media device. Once recorded, the user can move or space shift the TV program to another digital media device; however, he is prevented from copying that program to another device (i.e., only a single digital example of the TV program can be stored at one time). For example, if a TV program is recorded to a hard disk recorder, “copy-once” mode will allow the user to move that content to another copy-protected digital media device such as D-VHS. This shift of storage medium tags the moved content as “copy-one generation”. The content can continue to be moved, but not copied, between copy-protected media digital devices. It is important to note, however, that “copy-once” mode does not prohibit all types of copying. It is possible to copy TV programs to analog media devices such as standard VHS. Currently , there is ongoing research in Japan into new modes such as “copy 9” and a home networking solution to enable more accurate copy control for digital broadcast.

In addition to copy protection, the content protection encryption solution can also be used to enable regional control of viewing. By distributing different decryption keys to set-top boxes in different areas, different programming can be made available to users located in different regions. This encryption-based solution is also used by Japanese broadcasters for pay TV. Only subscribers who sign a contract with a broadcaster receive decryption keys for the paid programming.

The Conditional Access System (CAS)

Technically, this content protection solution is implemented through a Conditional Access System (CAS). In general, a CAS is a system that protects content by requiring certain criteria to be met before access is granted. Japan’s CAS relies on a B-CAS card, which is an Integrated Circuit (IC) card, for such access.

The B-CAS card is required to decrypt all broadcasts. In Japan, these cards are included with every digital TV tuner or set-top box at no charge. To watch digital TV broadcasts, the B- CAS card has to be inserted in the set-top box. For the card to be operational, users are also required to agree to the terms and conditions of its use. User registration is also encouraged in order to fully enjoy interactive programming.

The CAS in Japan employs a robust encryption system. Each user receives a B-CAS card that has a unique master key that is stored in the tamper-resistant part of the card. This key is shared with broadcasters and is used to encrypt personal contract information when broadcasters transmit information to that user’s set-top box.

At the broadcasting station, content is scrambled with the use of a scramble key. The scramble key is then encrypted with a work key and the work key is then encrypted with a master key. The encrypted content and keys are then combined and transmitted to the user’s set-top box. This procedure is termed “three-step encryption”.

The user’s set-top box receives the encrypted content and keys, separating them into their components. It then sends the content and keys through the B-CAS card for decryption. Only then do users get to view and listen to the content.

Conclusion

As a whole, Japan’s content protection solution has been successful at safeguarding broadcaster copyrights resulting in few violations. With the nationwide digital TV coverage and the discontinuation of analog TV scheduled for 2011, broadcasters in Japan continue to refine and improve their content protection solutions.