Most video connection interfaces such as DVI, HDMI, and Display Port, include support for a technology called HDCP. HDCP, or High-bandwidth Digital Content Protection, is a copyright protection protocol that is used to encrypt data as it is being transmitted and to prevent copyrighted content from being played on unauthorized devices. By doing so it is intended to make it much harder to pirate copyrighted content. To make use of this, copyrighted content, such as movies on DVDs, instruct the playback device to utilize HDCP when playing their content. If an HDCP connection fails, the device will refuse to play the content.
HDCP was developed by Intel and requires device manufacturers to pay an annual licence fee and comply with a set of conditions. For example, an HDCP enabled device must not be designed to copy HDCP protected data, it must not transmit HDCP content to non-HDCP receivers, and it must “Frustrate attempts to defeat the content protection requirements”.
Weaknesses have been known to exist in the HDCP protocol, since the early 2000’s. In 2010 a master key was publicly leaked that could be used to create valid HDCP device keys. The master key was discovered through a reverse engineering process that exploited design flaws. If used the master key could allow the creation of apparently valid HDCP devices that implement HDCP in such a way that the protections are removed. Using the key, however, is considered to be complex as it would be necessary to be implemented in a custom silicon chip.
Issues with HDCP
A number of issues have been caused by HDCP. One issue is that it creates a way for an otherwise simple wired connection to fail. Each device is supposed to be configured with 40 keys so it can connect with up to 40 devices at once, unfortunately, not all devices do so. Some signal receivers implement a limited number of encryption keys which means that when configured in public environments such as bars, they can only be connected to a much smaller number of TVs.
Another issue is that HDCP incurs a small input delay due to the encryption and decryption processing. This negatively affects the experience when playing interactive media such as video games. The HDCP implementation on Apple laptops is always enabled, even when not required. This makes it unnecessarily difficult to record non-copyrighted content, including for example, simply using an external display for a presentation.