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HDCP, High –Bandwidth Digital Content Protection: Beginners Guide
 

Background:

High Definition digital video allows users to experience high resolution, near perfect video content. As more content is delivered digitally, the content creators are increasingly concerned with content piracy because digital content can be perfectly duplicated. Therefore anti-piracy safeguards such, as High Bandwidth Content Protection (HDCP) is necessary in order for original content creators to protect their assets. In this article we will touch on the key points of HDCP.

What is HDCP:

High-Bandwidth Digital Content Protection, HDCP, is an encryption scheme developed to defend against uncontrolled copying of digital content over high bandwidth digital interconnects such as DVI and the HDMI. The FCC approved HDCP as a "Digital Output Protection Technology" on August 4th, 2004.

A HDCP protected system consists of: 1) HDCP transmitter (DVD player for example), 2) the digital interface (DVI or HDMI), and 3) the HDCP receiver (your display monitor). In brief, the content is encrypted at the transmitter and the signal is passed to the HDCP receiver (display) via the DDC lines (in essence an I2C bus) where it is decrypted before viewing. HDCP requires that both the transmitter and the receiver comply with standards. If either one does not comply, the video will not be displayed properly. Incidentally, HDCP does not apply to analog interface such as component video although component video can be used to display high definition video.

Why should the consumer care about HDCP:

It is highly recommended that consumers be aware of HDCP and purchase sets that are HDCP compliant. Here is why. It has been speculated that the two competing high definition DVD standards HD DVD, and BLUE RAY, due out in 2006 will only deliver full resolution on HDCP protected outputs such as HDMI or DVI. If true, then users must have a HDCP monitor in order to experience full resolution HD DVD technology. Therefore it is prudent for the consumer to select HDCP compliant displays so the display can be used with future applications.

What is involved during a HDCP session:

HDCP is a complicated process but can be broken down to 3 key functions: Authentication, Encryption, and Renewability

Authentication: The first step before video is actually sent is for the HDCP transmitter to determine if the receiver is “authorized” to accept HDCP protected content. Stored in the PROM of each transmitter and receiver is an array of 40, 56-bit secret keys and a 40-bit entity called Key Selection Vector. Authentication requires that the transmitter and receiver pair exchange “secret keys” and key selection vectors. The keys are scrambled and never revealed. The math behind the encryption allows each half to calculate a resultant number, call it Rs, based on the key exchanges. The Rs value is then shared and compared. If the Rs value matches, the receiver is accepted as an authorized HDCP receiver and video transmission can start.

Encryption/Transmission: Once authentication is completed, transmission of the video content can commence. To prevent an unauthorized receiver from receiving the content, the video data must be encrypted prior to transmission. At the transmitter end, the video data bits are exclusive-ored with a shared calculated number lets call it Rt ( Rt is similar to how Rs was calculated) and sent to the receiver. At the receiver end the encrypted data is again exclusive-ored with Rt. Since the XOR function is invertible, XORing with the same Rt at the receiver end will reveal the true unscrambled video bits. Incidentally, a new Rt value is calculated about every 2 second to prevent corruption due to hacking.

Renewability: renewability futhur ensures that the private keys are not exposed to unauthorized users due to tampering.

Conclusion:

HDTV technology is changing rapidly. Content providers need to protect against piracy by implementing HDCP. HDCP and digital connection standards such as HDMI will become the de facto standard for digital video connections. We have outlined the important features of HDCP, so the consumer can make intelligent purchasing decisions.

References:

"High Bandwitch Digital Content Protection System" Rev. 1.1 9, June 2003

 

 

 

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