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High-bandwidth Digital Content Protection (HDCP) is a form of digital copy protection developed by Intel Corporation [1] to prevent copying of digital audio and video content as it travels across DisplayPort, Digital Visual Interface (DVI), High-Definition Multimedia Interface (HDMI), Gigabit Video Interface (GVIF), or Unified Display Interface (UDI) connections.

HDCP does not allow copying permitted by fair use laws. The system is meant to stop HDCP-encrypted content from being played on devices that do not support HDCP or which have been modified to copy HDCP content.[2][3] Before sending data, a transmitting device checks that the receiver is authorized to receive it. If so, the transmitter encrypts the data to prevent eavesdropping as it flows to the receiver.[4]

Manufacturers who want to make a device that supports HDCP must obtain a license from Intel subsidiary Digital Content Protection, pay an annual fee, and submit to various conditions.[5][6][7] For example, devices cannot be designed to copy content; devices must "frustrate attempts to defeat the content protection requirements";[7] high-definition digital video sources must not transmit protected content to non-HDCP receivers; and DVD-Audio content can only be played at CD-audio quality[7] by non-HDCP digital audio outputs (analog audio outputs have no quality limits).

Cryptanalysis researchers demonstrated flaws in HDCP as early as 2001, well before HDCP was deployed in any commercial product.Template:When In September 2010, an HDCP master key that can neutralize the key revocation feature of HDCP was released to the public.[8][9] Intel has confirmed that the crack is real,[10] and believes the master key was reverse engineered rather than leaked.[11] In practical terms, the impact of the crack has been described as "the digital equivalent of pointing a video camera at the TV", and of limited importance for pirates because the encryption of high-definition discs has been attacked directly, without the loss of interactive features like menus.[12] Intel threatened to sue anyone producing an unlicensed device.[11]


HDCP uses three systems:[5]

  1. Authentication prevents non-licensed devices from receiving content.
  2. Encryption of the data sent over DisplayPort, DVI, HDMI, GVIF, or UDI interfaces prevents eavesdropping of information and man-in-the-middle attacks.
  3. Key revocation prevents devices that have been compromised and cloned from receiving data.

Each HDCP-capable device has a unique set of 40 56-bit keys. Failure to keep them secret violates the license agreement. For each set of values, a special public key called a KSV (Key Selection Vector) is created. Each KSV consists of 40 bits (one bit for each HDCP key), with 20 bits set to 0 and 20 bits set to 1.

During authentication, the parties exchange their KSVs under a procedure called Blom's scheme. Each device adds (unsigned addition modulo 256) its own secret keys together according to a KSV received from another device. Depending on the order of the bits set to 1 in the KSV, a corresponding secret key is used or ignored in the addition. The generation of keys and KSVs gives both devices the same 56-bit number, which is later used to encrypt data.

Encryption is done by a stream cipher. Each decoded pixel is encrypted by applying an XOR operation with a 24-bit number produced by a generator. The HDCP specifications ensure constant updating of keys after each encoded frame.

If a particular set of keys is compromised, their corresponding KSV is added to a revocation list burned onto new discs in the DVD and Blu-ray formats. (The lists are signed with a DSA digital signature, which is meant to keep malicious users from revoking legitimate devices.) During authentication, the transmitting device looks for the receiver's KSV on the list, and if it is there, will not send protected content to the revoked device.


HDCP devices are generally divided into three categories:

The source sends the content to be displayed. Examples include set-top boxes, DVD, HD DVD and Blu-ray Disc players, and computer video cards. A source has only an HDCP/HDMI transmitter.[4]
The sink renders the content for display so it can be viewed. Examples include TVs and digital projectors. A sink has one or more HDCP/HDMI receivers.[4]
A repeater accepts content, decrypts it, then re-encrypts and retransmits the data. It may perform some signal processing, such as upconverting video into a higher-resolution format, or splitting out the audio portion of the signal. Repeaters have HDMI inputs and outputs. Examples include home theater audio-visual receivers that separate and amplify the audio signal, while re-transmitting the video for display on a TV. A repeater could also simply send the input data stream to multiple outputs for simultaneous display on several screens.[4]

Each device may contain one or more HDCP transmitters and/or receivers. (A single transmitter or receiver chip may combine HDCP and HDMI functionality.)[4]

In the United States, the Federal Communications Commission (FCC) approved HDCP as a "Digital Output Protection Technology" on August 4, 2004.[13] The FCC's Broadcast flag regulations, which were struck down by the United States Court of Appeals for the District of Columbia Circuit, would have required DRM technologies on all digital outputs from HDTV signal demodulators. Congress is still considering legislation that would implement something similar to the Broadcast Flag. The HDCP standard is more restrictive than the FCC's Digital Output Protection Technology requirement. HDCP bans compliant products from converting HDCP-restricted content to full-resolution analog form, presumably in an attempt to reduce the size of the analog hole.

On January 19, 2005, the European Information, Communications, and Consumer Electronics Technology Industry Associations (EICTA) announced that HDCP is a required component of the European "HD ready" label.[14]

Microsoft Windows Vista uses HDCP in computer graphics cards and monitors.[15][16]


HDCP strippers remove HDCP information from the video signal, allow the data to flow freely to a non-HDCP display.[17]


Well before HDCP was deployed in any commercial product,Template:When cryptanalysis researchers had demonstrated flaws in it.

In 2001, Scott Crosby of Carnegie Mellon University wrote a paper with Ian Goldberg, Robert Johnson, Dawn Song, and David Wagner called "A Cryptanalysis of the High-bandwidth Digital Content Protection System", and presented it at ACM-CCS8 DRM Workshop on November 5.[18]

The authors concluded that HDCP's linear key exchange is a fundamental weakness, and discussed ways to:

  • Eavesdrop on any data.
  • Clone any device with only its public key.
  • Avoid any blacklist on devices.
  • Create new device key vectors.
  • In aggregate, usurp the authority completely.

They also said the Blom's scheme key swap could be broken by a so-called conspiracy attack: obtaining the keys of 39 devices and reconstructing the secret symmetrical master matrix that was used to compute them.

Around the same time, Niels Ferguson independently claimed to have broken the HDCP scheme, but he did not publish his research, citing legal concerns arising from the controversial Digital Millennium Copyright Act.[19]

Master key release[]

On September 14, 2010, the Engadget website reported the release of a possible genuine HDCP master key which can neutralize the key revocation feature of HDCP.[8] It was not immediately clear who discovered the key or how they discovered it, though the discovery was announced via a Twitter update which linked to a Pastebin snippet containing the key and instructions on how to use it. Engadget said the attacker may have used the method proposed by Crosby in 2001 to retrieve the master key, although they cited a different researcher. On September 16, Intel confirmed that the code had been cracked.[20][21] Intel has threatened legal action against anyone producing hardware to circumvent the HDCP, possibly under the DMCA.[22]


HDCP can cause problems for users who want to connect multiple screens to a device; for example, a bar with several televisions connected to one satellite receiver. HDCP devices can create multiple keys, allowing each screen to operate, but the number varies from device to device; e.g., a Dish or Sky satellite receiver can generate 16 keys.[23] The technology sometimes causes handshaking problems where devices cannot establish a connection, especially with older high-definition displays.[24][25][26]

Edward Felten wrote "the main practical effect of HDCP has been to create one more way in which your electronics could fail to work properly with your TV," and concluded in the aftermath of the master key fiasco that HDCP has been "less a security system than a tool for shaping the consumer electronics market."[27]

Interface support by version[]

HDCP revision Supported interfaces
1.0 DVI
2.0 [Interface Independent Adaptation, Any IP based interface, compressed or uncompressed]


  1. Template:Cite web
  2. HDCP specification 1.3. Page 31 0x15, Page 35
  3. Template:Cite web 080509
  4. 4.0 4.1 4.2 4.3 4.4 (2008, July). HDCP deciphered: white paper. Retrieved July 22, 2008, from DCP, LLC. Web site:
  5. 5.0 5.1 Template:Cite web
  6. Template:Cite web
  7. 7.0 7.1 7.2 Template:Cite news
  8. 8.0 8.1 Template:Cite web
  9. Template:Cite news
  11. 11.0 11.1
  13. Template:Cite press release
  14. Template:Cite press release
  15. Output Content Protection and Windows Vista
  16. The Clicker: Microsoft's OPM for the masses - Engadget
  17. Template:Cite web
  18. Template:Cite conference
  19. Niels Ferguson, DMCA Censorship, August 15, 2001
  22. Wired. "Intel Threatens to Sue Anyone Who Uses HDCP Crack".
  24. PS3 Blinking Mystery Deepens—Westinghouse: "Our TVs Not the Problem" - Popular Mechanics
  25. HDCP "Handshake" A Big Problem For Many Legacy DVI-Based HDTVs
  26. Digital TV DesignLine | HDMI/DVI HDCP handshake problems & how to avoid them

External links[]

Template:Broadcast encryption

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