Digital Content Protection HDCP Compatible Test Secret


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HDCP (High-Bandwidth Digital Content Protection) is a technology developed by Intel subsidiary Digital Content Protection LLC (DCP) to protect digital entertainment content to ensure that digital video and audio data are transmitted through the transmission interface. It will not be illegally copied when it is transmitted. The HDCP specification is protected by a number of patents. The standard set for high-resolution products cannot completely eliminate the content copying problems faced by the digital age, but the products have been designed to increase the threshold and cost of counterfeiters. The idea of ​​most crackers. With the increasing popularity of HDCP products, the era when we seem to be able to smell high resolution has officially arrived.

Rigorous encryption mechanism

The protection mechanism of HDCP includes three elements: (1) HDCP transmitter (Transmitter/Source), which can immediately authenticate the downstream connection to the receiver. The authentication protocol ensures that the signal sent by the HDCP transmitter is authorized by the HDCP receiver. . (2) DCP LLC will revoke the authorization of the invalid HDCP receiver. (3) While transmitting and receiving under the HDCP-protected signal, the video content is continuously verified.

In addition, manufacturers who want to apply HDCP technology to their products must first become DCP members (US$15,000 for membership fees) and obtain authorization. The authorization levels are classified according to the degree of development of the products. Only the fully licensed vendor can obtain a unique key set (called KSV) to develop or sell the product. This authorization password will be recorded in the DCP. Once the authorized vendor member expires, its KSV will be marked in the DCP database as Revoke the key.

The data content protected by the HDCP technology on the computer platform is first verified by the COPP (Certified Output Protection Protocol) device in the operating system, and only the legitimate video card can display the content. The KSV of the display device is then authenticated, and only devices that comply with the HDCP requirements can display the content delivered by the display card. When the sender is connected to the receiver, a set of Secret Values ​​known only to both parties is generated to ensure that the connection is legitimate and cannot be copied. HDCP will rely on this Secret Value in the process of encryption or decryption. Only the sender and receiver after the synchronization can be reversed to complete the data restoration. The HDCP system will also compare and look up in the revocation list after receiving the KSV value. The KSV appearing in the list will be considered illegal, causing the authentication process to fail.

HDCP data validation is divided into three levels: First Part, Second Part and Third Part (called Link Integrity Check in DisplayPort; this point will be discussed when discussing the differences between HDMI HDCP and DisplayPort HDCP). The aforementioned Secret Value will be verified at the First Part, and the sender and receiver will exchange their KSV with each other and generate a Secret Value. The Second Part is for the Repeater Device, which verifies all downstream receivers, generates their corresponding Secret Values ​​and returns upstream. If the sender or receiver changes, the Repeater's HDCP mechanism will generate a new Secret Value and re-verify to prevent the copy machine from inserting it to retrieve data. At Third-Part, the HDCP system will confirm whether the frequency and sequence of data encryption or decryption of the two HDCP devices are consistent and synchronized, and generate additional verification code verification while data is being transmitted.

With this layer of protection, consumers want to play HDCP-protected audio and video content such as Blu-ray Disc, PlayStation 3 games, signal source (player or computer display card) and both sides of the display must have built-in HDCP KSV Normal play. If any of the system does not have a built-in KSV, you cannot use high-resolution playback or even play back images.

Compatible test development

The HDCP Compliance Test, developed by DCP LLC, provides an effective conduit for operators using HDCP specifications to ensure that the products they develop are compliant with HDCP specifications. In addition to the compatibility specifications originally developed under the HDMI specification, the HDCP test of DisplayPort has been added this year with the introduction of the VESA DisplayPort compatible certification test. Currently Authorized Testing Center (ATC) includes DCP, LLC HDCP Lab, Allion Test Labs, Matsushita Electric Industrial Co., Ltd, NXP Semiconductors, Silicon Image and Sony, of which only At the same time, compatible certification tests for HDMI HDCP and DisplayPort HDCP can be performed. Although there is no logo certification in this test, HDMI and VESA Association strongly recommend that manufacturers implement HDCP compatibility testing, so that the tested products can be listed on the DCP website in response to the market's protection mechanism for high-resolution products. Sexual needs.

HDCP sets different test procedures depending on the device type. All HDCP inputs and outputs on the device must be tested for compatibility. In each device category, different levels of testing must be performed for various DUTs. For the Transmitter/Source and Receiver/Sink, it is necessary to test the synchronization of the KSV value exchange verification and the establishment of communication bridge. The Repeater test includes all tests in the transmitting device and the receiving device, and is required to check the authentication protocol capabilities of the receiving device (Repeater or Receiver) of the downstream plurality.

HDCP Transmitter (Transmitter/Source) test

Use the test instrument to simulate the downstream Sink or Repeater of the Source to verify the HDCP behavior of the Source. If there is re-verification after hot plugging (HPD).

Digital Content Protection HDCP Compatible Test Secret

HDCP receiver (Receiver/Sink) test

Use the test instrument to simulate the upstream connection source of the Sink to verify the HDCP behavior of the receiver. If it can correctly generate Secret Value.

Digital Content Protection HDCP Compatible Test Secret

HDCP Repeater test

The test of the repeater is the most complicated, and it needs to verify its HDCP function as Source or Sink, as well as its own HDCP function of the repeater.

(1) Verify the function of its transmitter

The tested HDCP Source device is used as the signal source of the Repeater, and the test instrument is used to simulate the Sink device with another Repeater device to verify the HDCP behavior of the Repeater in transmitting the signal.

Digital Content Protection HDCP Compatible Test Secret

(2) Verify the function of its receiver

The test device is used to simulate the Source device to send a signal to the Repeater, and then verify whether the function of the single or multiple sets of Sink devices sent by the Repeater to pass the test is normal, or replace the Sink device in operation, and whether the Repeater can re-execute the HDCP verification.

Digital Content Protection HDCP Compatible Test Secret

(3) Verify the function of its repeater

In the HDCP test, the Repeater acts as the commander of the Commander-in-Chief, which must control the number of devices connected downstream and confirm that it meets the specified limits. The number of connection layers from upstream to downstream (Source to Sink) is up to eight, and the number of devices with the total connection of Source is up to 128. In addition to the measurement of depth and breadth, it is also necessary to verify its own functional parameters.

Digital Content Protection HDCP Compatible Test Secret

Difference between HDMI HDCP and DisplayPort HDCP test

There are some differences in the test specifications between HDMI HDCP and DisplayPort HDCP. In addition to the different test instruments approved by the association, the test definitions and limitations are not the same. The only HDMI HDCP test instrument authorized by DCP LLC is Panasonic Ulta2000; the DisplayPort HDCP test instrument is QuantumData882E-DP. The HDMI object to be tested needs to support any of the VGA, 480p, and 576p display formats in RGB mode, while DisplayPort accepts any form of format. As for the aforementioned Third Part authentication level, the DisplayPort HDCP is called Integrity Check, which is the biggest difference between HDMI and DisplayPort. DisplayPort's Link Layer is responsible for confirming the link performance and correct communication between the two devices. The parameter value (0=complete, 1=incomplete) is used as the communication language. The difference with HDMI's Third Part is the different encryption. Decryption verification method.

Digital Content Protection HDCP Compatible Test Secret

The challenge of HDCP

At present, there are many types of HDMI products certified by HDCP, and most of them are CE products such as TV, Monitor and Blu-ray drive. At present, no PC products have passed the test. The reason is that the transmission of data is relatively simple in CE products, but when it encounters the complex interface of PC, the interaction between many factors (OS, software, display card, Blu-ray drive) will affect the test results and judgment. A vulnerability in encryption and decryption by a factor (such as OS) increases the likelihood of data leakage during overall operation. The HDCP specification will have the popularity of PCs and the protection of digital content in the future. It is also necessary for system vendors and manufacturers to cooperate with each other. It seems that there are still vulnerabilities that have been cracked by the existing specifications.

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