Discuss their effects on digital transmission
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Digital Transmission
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Integrated Services Digital NetworkTelecommunicationTime Division Multiple Accessvoice activity detectionDigital SignalTelevision Signal
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Digital Set-Top Terminals and Consumer Interfaces
Walter Ciciora, ... Michael Adams, in Modern Cable Television Technology (Second Edition), 2004
IEEE 1394 and DTCP
The digital transmission content protection (DTCP) standard for secure transmission over IEEE 1394 physical links was developed by five companies — Intel, Matsushita (Panasonic), Toshiba, Sony, and Hitachi — and is thus sometimes called the “5C” content protection scheme. 1394 is intended as a broader-use standard than is DVI, being intended not only for transmission to a display or displays, but also for transfer to recording devices, computers, and whatever other devices you wish. DVI transfers uncompressed (hence very wideband) red, green, and blue data for immediate display; IEEE 1394 transmits compressed (therefore lower bandwidth) data.
DTCP, the associated verification and encryption standard, includes the same elements as does HDCP, with one more. It includes authentication and key exchange (AKE), transmission, referred to as content encryption, and renewability. It also includes a new element, copy control information.
DTCP includes instructions to the receiving device as to how it should treat the data. This is called copy control information, CCI, which is embedded in the content. The actual data in the CCI is known as the encryption mode indicator (EMI). It may take on any of four states. The material may be used for unlimited copying, copy free, and the opposite state, copy never. Another state is copy once, such as to allow for time shifting a TV program. When the material is played, the EMI is changed to copy no more. These last two values of the EMI are intended for devices with limited computational ability. The associated limited, or restricted, authentication required involves fewer computations than does full authentication.
Obviously, the same concerns apply here as to other systems. Every device licensed to receive material protected by DTCP must obey these rules. Thus, the same need exists for a trusted authority to certify each device. DTCP is administered by the Digital Transmission Licensing Administrator (DTLA), established by the five companies. The DTLA acts as the certificate authority (CA) for conformant devices. Besides the CCI, DTCP includes authentication and key exchange, content encryption, and renewability.
Two levels of authentication and key exchange are specified: Full authentication using public key cryptography as described earlier is used for all types of content. For copy once and copy no more content, a more limited, restricted authentication using common key cryptography is permitted.
For full authentication, the method is similar to, but uses different formats than, that described in Section 22.5.3.25 A certificate is embedded in each device and is verified as described earlier. Both the source device (supplying the content) and the sink device (receiving the content) check the other device's certificate. A form of Diffie-Hellman key exchange is used for derivation of a secret key used to encrypt program material. Restricted authentication may use a short form of authentication, where the sink device proves that it shares a secret with the source device.26
After authentication, the source device (the host) sends an exchange key, encrypted with the authentication key, to the sink device. This exchange key is sent as a seed, a random number generated by the source, from which both devices can compute the decryption key. The key is changed periodically, every 30–120 seconds.
In order to provide for system renewability, system renewability messages (SRMs) are sent to each IEEE 1394-compliant device. These may be sent as part of a program stream from a headend, or they may be incorporated into other distribution media, such as DVDs. The SRMs carry identification of any device that has had its certificate revoked. As material containing the identification propagates throughout the nation, devices eventually.
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