System is an integrated system, the system involves a variety of techniques, including encryption technology, plus descrambling technology, coding, multiplexing, Smart Card Technical, network technology, access technology, in addition related to user management, program management, fees management, information management technologies.
Conditional access is Digital TV Encryption to ensure the control of core technology for digital TV Operation Provided the necessary technical means to have a legitimate use of authorized users of a particular business, while unauthorized users can not use this service.
Conditional access system is based on MPEG -2 And DV B Standard Development and design and in line with the development of digital TV SARFT Broadcasting Conditional access system specifications.
Digital video broadcast standard DVB (Digitial Video Broadcast) is a digital television General International standards, DVB standard to MPEG-2 encoding system for the base, using the MPEG-2 data packet structure as the data container, and use the strict format of DVB service information effectively and conveniently transfer between various media and Implementation of digital signal conversion between them. Applications related to satellite transmission, Cable Transmission, terrestrial transmission.
DVB scrambling in two ways, namely with the density (SimulCrypt) and more dense (MultiCrypt). With the density requirements can use multiple front-end CA systems, each CA system can be encrypted using different encryption systems their information, but program content scrambling to adopt the same scrambling algorithm and processing interference control word, this will ensure receiver using a different receiving device while receiving the same digital television programs. Using the same secret techniques, you can easily manage multi-operator, multi-carrier choice for the conditional access system provides flexibility. The multi-secret technology mainly for the purposes of the receiver, the user can use more intensive way of receiving a different scrambling / encryption system to encrypt the different programs. As the DVB in secret with the more dense with all the provisions of the standard interface, thus facilitating the integration of multiple CA systems, but also convenient for users.
Those prevailing in the international on the DVB standard in Europe, North American ATSC standard and the Japanese ISDB standard. In the three standard parts for the CA requirements were simple and made three different scrambling methods. European DVB Organization A common scrambling algorithm called (Common ScramblingAlgorithm) of the scrambling mode, the DVB organization authorized by the four member companies, ATSC organizations use a common DES algorithm three-Diego, and the Japanese made use of a Panasonic kind of scrambling algorithms.
2, Conditional Access System Principles In principle about before about two in the CA equipment is easy to confuse the concept: a Deinterference (Scrambling-Descrambling), the other is the encryption (Encryption-Decryption). Deinterference technology is used to control the sending end CA system to change or control the delivery of services (programs) of certain characteristics, so that unauthorized users can not access the service provider's interests; and cryptographic techniques are used to In the transmitter to provide an encrypted message, so that the client authorized descrambler in order to be able to decrypt the data, this information by the CA system control and configuration in encrypted form in the transport stream information to prevent unauthorized users to use the information for descrambling, different CA systems management and information delivery method that is very different.
Simply is: Scrambling through the control word (CW, Controlword) on the transport stream bit-encryption process, encryption part of the actual completion of the control word (CW) protection. These two techniques is an important part of CA systems, the technical similarities, but the standard in the CA system is the independence of strong two parts.
In the current conditions of the various standards organizations to receive standard, some scrambling often seek unity in the encryption part is generally not specified, is defined in part by the manufacturer.
Conditional access control word CW is the core of transmission control. The introduction of MPEG-2 standard digital television system, and the program stream conditional access system has two data flow related to: authorization control information ECM (Entitle Control Message) and authorization management information EMM (Entitle ManageMessage). The business key SK (ServiceKey) after the CW encrypted to send in the ECM, ECM also includes program source, time, content classification and program price program information. SK encryption on CW to send the EMM, and SK before sending individuals to go through the distribution of key PDK (PersonalDistribute Key) encryption processing, EMM also includes addresses, user authorization information.
Initial control word (CW) for descrambling key to use. Descrambling key is the basic element of system security. End of the CW itself (as well as other parts of system data) to use an encryption key is encrypted by encryption algorithm to protect it, the encryption key is used to change a result of any number of encryption algorithms. Fixed the key is not applicable (poor security), changes in the key should be used by CA controllers or other natural means of artificial generate a new random number. In specific applications, usually generated by the service providers to control their services, so call it business keys SK. SK's use and users pay conditions. Although
CW encrypted by the SK, but the key is still available if anyone reads, network operators, or difficult to control to a specific user, or security problems must be encrypted to protect SK again. As the shared network addressing mode address packet is sent by the user, each device has a unique address does not duplicate code, address code can be used to encrypt on the SK.
In actual use, the address of the terminal equipment is generally open, and basically unchanged, so often used and the address code associated with a number of columns to be encrypted, as individuals are assigned key (PDK). PDK general system equipment automatically generated by the CA and strictly control the terminal equipment by the Department of the serial number of the general CA systems by network operators to provide special equipment for burning the PROM into the descrambler, and can not read out. A CA system are assigned to each user several PDK, to meet the extensive business needs.
Operators end-user encryption License There are many, and smart card authorization form is STB The mainstream market, has also been identified in China SARFT standard for our network equipment components.
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