Know The Lingo — What Is HDCP?

By: Joseph D. Cornwall, CTS-D
Technology Evangelist — C2G

Technical lingo is a kind of shorthand that's used to express concepts common to that specific topic or area of study. Technical lingo is important because it provides a very precise or unique "shorthand" description of a device, effect or concept. Unfortunately, if you aren't comfortable and familiar with the lingo of a topic it can be a tall hurdle to communicate efficiently with folks who consider the jargon of their field to be "self-explanatory." In this series of articles we'll lift the veils of misunderstanding from the lingo of the A/V industry.


High-bandwidth Digital Content Protection (HDCP; commonly, though incorrectly, referred to as High Definition Copy Protection) is a form of digital copy protection developed by the Intel Corporation to prevent unauthorized duplication of digital audio and video content as it travels between devices in the last 100 meters of an installation. HDCP is used in DisplayPort (DP) and Digital Visual Interface (DVI) connections, though it is most commonly associated with High Definition Multimedia Interface (HDMI).

The proliferation of digital audio and video content brought with it a somewhat unexpected problem. In the analog domain, every time a copy is made of a program a little bit of the quality of the content is lost—noise is added, and detail is softened. This isn't true in the digital world, where a copy of the 1's and 0's that make up the data is essentially an indistinguishable clone. To protect the rights of the content owners (often referred to as "digital rights management"), a system that effectively hindered illicit copying was needed.

There are a number of copy protection systems that operate at the programming level. They range from conditional access systems deployed in large-scale satellite network broadcasts to CSS, AACS and other proprietary systems that protect content during delivery. A single system is necessary to provide a standardized content protection scheme while the content is being transferred from its source device (satellite receiver, cable set-top box, DVD player, or streaming media player such as TIVO or PS3) to a display device. HDCP fulfills that role. It is managed by Digital Content Protection LLC, a division of Intel. HDCP compliance is ubiquitous, global and mandatory if protected content is to be legally accessed. What's more, there is no legally permissible way to convert HDCP encrypted content back to an analog (unprotected) state; this is clearly stated in the Digital Millennium Copyright Act of 1998.

HDCP uses a cryptographic technique known as Blom's Scheme, a form of threshold secret sharing. In HDCP systems each device has both a secret key and a public identifier. When both devices successfully exchange public keys, they are able to create a shared key for communicating. This is what is meant by "key authentication and exchange." As you might surmise, HDCP compliance is impossible with an analog connection or analog device attached to the system.

Source devices like TIVO DVR's, DVD players, laptop computers, and satellite receivers all use HDCP copy protection to prevent illicit duplication of encrypted content. Displays such as LCD flat panels, projectors, and plasma screens (collectively known as "sink" devices) must have HDCP compliance capability for the system to work. A third class of devices, such as switchers, selectors, extenders, and splitters (collectively known as "repeater" devices) also have HDCP components. One of the inherent abilities of HDCP is that it can examine every device connected to the A/V network and prevent any transmission of signal if even a single device is found to be non-compliant.

There are two possible responses an HDCP-enabled system can exhibit when faced with attached noncompliant components. The system can show the content with a highly reduced resolution (480i) if the content is encoded with an Image Constraint Token (ICT). Alternately, the system can show a blank screen (typically solid blue or black) if the content is encoded with a Digital Only Token (DOT).

Most currently deployed implementations of HDCP are using version 1.4. New hardware devices, particularly those featuring Miracast capability, will be using the recently released HDCP v2.2.

This white paper is for informational purposes only and is subject to change without notice. C2G makes no guarantees, either expressed or implied, concerning the accuracy, completeness or reliability of the information found in this document.