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High-bandwidth Digital Content Protection (HDCP), is a form of digital copy protection developed by Intel Corporation to prevent copying of digital audio and video content as it travels across connections. Types of connections include DisplayPort (DP), Digital Visual Interface (DVI), and High-Definition Multimedia Interface (HDMI), as well as less popular, or now defunct, protocols like Gigabit Video Interface (GVIF) and Unified Display Interface (UDI). The system is meant to stop HDCP-encrypted content from being played on unauthorized devices or devices which have been modified to copy HDCP content.〔HDCP specification 1.3. Page 31 0x15, Page 35〕〔 080509 hddvd-faq.com〕 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.〔 In order to make a device that plays material protected by HDCP, the manufacturer must obtain a license from Intel subsidiary Digital Content Protection LLC, pay an annual fee, and submit to various conditions.〔(【引用サイトリンク】title=Digital Content Protection LLC )〕 For example, the device cannot be designed to copy; it must "frustrate attempts to defeat the content protection requirements";〔 it must not transmit high definition protected video to non-HDCP receivers; and DVD-Audio material can be played only at CD-audio quality〔 by non-HDCP digital audio outputs (analog audio outputs have no quality limits). Cryptanalysis researchers demonstrated flaws in HDCP as early as 2001. In September 2010, an HDCP master key that allows for the generation of valid device keys—rendering the key revocation feature of HDCP useless—was released to the public. Intel has confirmed that the crack is real,〔(Intel confirms that HDCP has been cracked- The Inquirer )〕 and believes the master key was reverse engineered rather than leaked.〔 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 copyright infringers because the encryption of high-definition discs has been attacked directly, with the loss of interactive features like menus.〔(HDCP antipiracy leak opens doors for black boxes | InSecurity Complex - CNET News )〕 Intel threatened to sue anyone producing an unlicensed device.〔Wired. "(Intel Threatens to Sue Anyone Who Uses HDCP Crack )".〕 == Specification == HDCP uses three systems:〔 #Authentication prevents non-licensed devices from receiving content. #Encryption of the data sent over DisplayPort, DVI, HDMI, GVIF, or UDI interfaces prevents eavesdropping of information and man-in-the-middle attacks. #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 its own secret keys together (using unsigned addition modulo 256) 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「High-bandwidth Digital Content Protection」の詳細全文を読む スポンサード リンク
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