Understanding HDCP

Will the new Windows stop you from watching your movies?

Do you rip your DVD movies? Chances are, if you are like many of us, when you purchase a movie you like to keep it in good condition. It's not uncommon to rip or descramble DVD content to back it up, or play the stream directly from a local hard disk. This was all made possible by a young man by the name of Jon Lech Johansen (more widely known as DVD-Jon). Jon was instrumental in reverse engineering the protection methodologies in DVD content so that end users could rip to hard disk, and to save their pressed media from destruction. And in fact, without this, Linux users wouldn't even be able to play DVDs under Linux at all.

For several years now we have lived in comfort, knowing that if we have a DVD movie and want to play it from our hard disk or put it onto a different media-type, things just work. In an effort to circumvent the possible use of decoding and ripping DVDs for piracy Hollywood has, in conjunction with technology partners such as Macrovision, Intel and the Digital Content Protection LLC, put into motion a new set of content protection methods which are already being implemented and set to come into effect full force in the near future.

These copy protection methods, falling under an umbrella name of HDCP (High Bandwidth Digital Content Protection), not only stop the end user ripping media from a disc as with the original DVD copy protection mechanisms, but also takes this one step further and prevents any copy protected material even being displayed by a monitor.

Copy protection has, for all intents and purposes, moved from the software to the hardware. While HDCP still needs operating system support to operate, it also requires HDCP compliant devices in order to display HDCP protected material. It doesn't matter if you are the original owner of a protected DVD, without compliant HDCP equipment you won't be able to enjoy your purchase.

So what exactly is HDCP and how does it work? And more to the point, what is to become of your soon-to-be-obsolete equipment?

Defining HDCP
HDCP is was originally developed by Intel as a protocol to protect high definition content transferal across DVI (Digital Visual Interface) and HDMI (High Definition Multimedia Interface) interconnections. The protocol has been in existence since September 1999, when the first specification document was released. It is now up to revision 1.2a, as of May 10th 2006.

The purpose of HDCP is to prevent the end user viewing or ripping high definition content on non-authenticated devices. This high definition content generally comes in three forms:

1. HD-DVD (High Definition DVD) or BD-ROM (Blue-Ray Disc) movie discs;

2. High definition digital television broadcast signals/digital cable set-top transmissions;

3. High definition VGA card sources (games, movies, other content direct from the PC to the digital display panel).

HDCP achieves content protection through the use of a key-exchange infrastructure. One of the key (yes, a pun) features of this is the ability to revoke keys from devices manufactured by vendors who violate license agreements between the content producer and the display device producer.

Here's a practical example: If the end user attempts to play back a HD-DVD or BD-ROM movie on their PC, using simple software hacks (think of it like using a version of AnyDVD on steroids!), the system can report back to the central key-authority, revoking and black-listing the keys used on the user's PC, thus rendering it useless for all current and future playback, within this configuration.

Attempting to use these software bypass methods will result in a blank screen, or a message saying that an illegal attempt has been made to display content on a non-compliant system. Now this said this assumes that all the companies, vendors and stake-holders agree that this level of network connectivity/awareness is acceptable. As it is this level of control is still in the fetal stage of development, but it is possible with HDCP.

Fig. 1: Basic connection topology of a HDCP system

Get on the bandwagon
Not surprisingly, the introduction of HDCP hasn't been well met by all parties especially in regards to computing/information devices. A list has been compiled of current HDCP licensees who will implement the protocol according to the Intel specification.

This significant list of companies (approximately 368 at last update) represents all those willing to use HDCP in an effort to prevent content ripping and digital transferal of media other than for the exclusive private use of the end user, on a stand-alone dedicated, authenticated hardware platform. The key drivers in implementing the protection on the Hollywood movie studios side are Warner Brothers and the Walt Disney Company. This will translate to all Warner Brothers or Disney based movies (whether it be BD-ROM or HD-DVD) being in some way protected or locked down via HDCP. What of the other movie studios and companies? At this stage, they are yet to jump onboard, somewhat wisely waiting for the reactions of the general public, before making commitment to what amounts to a largely unknown Digital Rights Management technology.