High definition digital video allows users to experience near perfect high resolution video content. As more content is delivered digitally, content creators are increasingly concerned about content piracy because digital content can be perfectly duplicated. Therefore, anti-piracy security measures such as High Bandwidth Content Protection (HDCP) are necessary 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 HDMI. The FCC approved HDCP as “Digital Output Protection Technology” on August 4, 2004.
An HDCP protected system consists of: 1) the HDCP transmitter (DVD player, for example), 2) the digital interface (DVI or HDMI), and 3) the HDCP receiver (your screen monitor). In short, content is encrypted at the transmitter and the signal is passed to the HDCP receiver (display) via DDC lines (essentially an I2C bus) where it is decrypted before viewing. HDCP requires that both the transmitter and receiver comply with the standards. If either of the two does not comply, the video will not display correctly. By the way, 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 be concerned about HDCP?
It is strongly recommended that consumers become familiar with HDCP and purchase HDCP compliant equipment. Here’s why. It has been speculated that the two competing high definition DVD standards, HD DVD and BLUE RAY, coming out in 2006, will only offer full resolution on HDCP protected outputs such as HDMI or DVI. If true, users must have an HDCP monitor to experience full resolution HD DVD technology. Therefore, it is prudent for the consumer to select HDCP compliant displays so that the display can be used with future applications.
What is involved during an HDCP session:
HDCP is a complicated process but it can be divided into 3 key functions: Authentication, Encryption and Renewal
Authentication: The first step before the video is sent is for the HDCP transmitter to determine if the receiver is “authorized” to accept HDCP protected content. A set of 40 56-bit secret keys and a 40-bit entity called the Key Selection Vector are stored in the PROM of each transmitter and receiver. Authentication requires the transmitter and receiver pair to exchange “secret keys” and key selection vectors. The keys are encrypted and are never revealed. The math behind encryption allows each half to calculate a resulting number, call it Rs, based on the key exchanges. Then the value of Rs is shared and compared. If the value of Rs matches, the receiver is accepted as an authorized HDCP receiver and video transmission can be started.
Encryption / Transmission: After the authentication is complete, you can start streaming the video content. 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 unique with a shared calculated number, let’s 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 with Rt. Since the XOR function is invertible, XOR with the same Rt at the receiver end will reveal the true unencrypted video bits. By the way, a new Rt value is calculated approximately every 2 seconds to avoid corruption due to hacking.
Renewability: Renewability Futhur ensures that private keys are not exposed to unauthorized users due to tampering.
HDTV technology is changing rapidly. Content providers must protect against piracy by implementing HDCP. HDCP and digital connection standards like HDMI will become the de facto standard for digital video connections. We have outlined the important features of HDCP so that the consumer can make smart purchasing decisions.