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24 Everything You Ever Wanted to Know About DVD<br />
encrypted with a 56-bit C2 (Cryptomeria) cipher derived from the media ID.<br />
During playback, the ID is read from the BCA and used to generate a key to<br />
decrypt the contents of the disc. If the contents of the disc are copied to<br />
other media, the ID will be absent or wrong, and the data will not be<br />
decryptable.<br />
Digital Copy Protection System (DCPS)<br />
In order to provide digital connections between components without allowing<br />
perfect digital copies, five digital copy protection systems (DCPs) were<br />
proposed to the Consumer Electronics Association (CEA). The frontrunner<br />
is Digital Transmission Content Protection (DTCP), which focuses on IEEE<br />
1394/FireWire, but it can be applied to other protocols. The draft proposal<br />
(called 5C, for the five companies that developed it) was made by Intel,<br />
Sony, Hitachi, Matsushita, and Toshiba in February of 1998. Sony released<br />
a DTCP chip in mid-1999.<br />
Under DTCP, devices that are digitally connected, such as a DVD player<br />
and a digital TV or a digital VCR, exchange keys and authentication certificates<br />
to establish a secure channel. The DVD player encrypts the encoded<br />
audio-video signal as it sends it to the receiving device, which must decrypt<br />
it. This keeps other connected but unauthenticated devices from stealing<br />
the signal. No encryption is needed for content that is not copy protected.<br />
Security can be “renewed” by new content (such as new discs or new<br />
broadcasts) and new devices that carry updated keys and revocation lists<br />
(to identify unauthorized or compromised devices).<br />
A competing proposal, extended conditional access (XCA), from Zenith<br />
and Thomson, is similar to DTCP. However, it can work with one-way digital<br />
interfaces (such as the EIA-762 RF remodulator standard) and uses<br />
smart cards for renewable security. Other proposals have been made by<br />
MRJ Technology, NDS, and Philips. In all five proposals, content is marked<br />
with CGMS-style flags of “copy freely,” “copy once,” “don’t copy,” and<br />
sometimes “no more copies.” Digital devices that do nothing more than<br />
reproduce audio and video will be able to receive all data (as long as they<br />
can authenticate that they are playback-only devices). Digital recording<br />
devices can only receive data that is marked as copyable, and they must<br />
change the flag to “don’t copy” or “no more copies” if the source is marked<br />
“copy once.”<br />
DCPS in general is designed for the next generation of digital TVs,<br />
receivers, and video recorders. It requires new DVD players with digital<br />
connectors (such as those on digital video equipment). These new products<br />
began to appear in 2003. Because the encryption is done by the player, no<br />
changes are needed to existing discs.
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