By PURPLELEC | 05 January 2024 | 0 Comments
What is HDCP protocol
HDCP is the abbreviation of High-bandwidth Digital Content Protection, which can be called "HDCP Digital Content Protection" in Chinese. HDCP technology was jointly developed by Hollywood and semiconductor giant Intel. It can be actually used between transmission ends such as graphics cards and DVD players, as well as between the receiving ends of monitors, TVs, and projectors. It is an important anti-piracy technology for high-definition movies and TV programs. Monitors that do not support the HDCP protocol cannot normally play copyrighted high-definition programs.
High-definition movie programs after DVD use HDCP and AACS anti-piracy technology. Blu-ray and HD DVD both use this anti-piracy technology, and high-definition television (HDTV) will also use it. After using HDCP and AACS anti-piracy technology, movie programs can only be played normally on devices that support HDCP. Otherwise, you will only see a black screen or a low-quality display (the resolution is only about a quarter of the normal), which is inconvenient. The value of HD is lost. AACS is an encryption technology that is used in both HD DVD and Blu-ray discs to protect the video content on the disc from being copied and played elsewhere.
The HDCP protocol is used to prevent video content from being completely copied during the transmission process. This technology does not prevent digital signals from being illegally recorded, but encrypts digital signals so that illegal recording methods cannot achieve the original high-resolution image quality. For example, a Blu-ray disc player cannot record clear programs at the same time when playing a high-definition disc, and it cannot record clear programs on the monitor when playing a disc on a computer.
HDCP protects video signals from beginning to end, which means that every link in the entire playback system must support the HDCP protocol. If the monitor does not support the HDCP protocol, it will not be able to play high-definition programs normally and will only see a black screen or low image quality. program. To support the HDCP protocol, digital video interfaces such as DVI and HDMI must be used. Traditional analog signal interfaces such as VGA cannot support the HDCP protocol.
When using analog signal interfaces such as VGA, the picture will drop to low quality, or it will prompt that it cannot be played, thereby losing the meaning of high definition and preventing piracy. It should be noted that the HDMI interface has the HDCP protocol embedded in it, and all displays with HDMI interfaces support the HDCP protocol. However, not all LCD monitors with DVI interfaces support the HDCP protocol. They must be certified monitors with corresponding hardware chips.
When the data content protected by HDCP technology on the computer platform is output, the COPP driver (Certified Output Protection Protocol) in the operating system will first verify the graphics card. Only legal graphics cards can realize content output, and then the key of the display device must be authenticated. Only devices that meet HDCP requirements can ultimately display the content sent by the graphics card.
During the HDCP transmission process, both the sender and the receiver store a set of available keys. These keys are stored secretly. Both the sender and the receiver perform encryption and decryption operations based on the keys. A special key must be added to this operation. Value KSV (Video Encryption Key). At the same time, each HDCP device will have a unique KSV sequence number. The cryptographic processing units of the sender and the receiver will check each other's KSV value to ensure that the connection is legal. The encryption process of HDCP will process each pixel, making the picture irregular and unrecognizable. Only the sender and receiver after confirming synchronization can perform reverse processing and complete data restoration. During the decryption process, the HDCP system will confirm the connection every 2 seconds, and synchronize the sender and receiver identification codes every 128 frames to ensure synchronization of the connection.
In order to deal with the situation of key leakage, HDCP has specially established a "key revocation" mechanism. The key set KSV value of each device is unique. After receiving the KSV value, the HDCP system will compare and search it in the revocation list. The KSV that appears in the list will be considered illegal, causing the authentication process to fail. The revocation key list here will be included in the HDCP corresponding multimedia data and will be updated automatically.
It can be seen that in order to play copyrighted high-definition programs on a computer, whether it is HDTV, Blu-ray or HD DVD discs, the monitor and graphics card are required to support the HDCP protocol. However, if manufacturers want to put the HDCP logo on their products, they need to pay a certain certification fee and add hardware chips, which obviously increases the cost. Currently, only some products have passed the certification. As high-definition programs will gradually become more popular, HDCP has become a foregone conclusion, so more and more devices will support the HDCP protocol.
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