What is the CA(Conditional Access) for a Digital TV?
Digital TV CA is the English abbreviation of digital TV conditional access (Conditional Access).
With the development of TV technology towards digital video broadcasting, more and more advanced computer network communication technologies are applied in digital TV technology. Conditional Access (CA) technology plays an important role in the application of digital TV platform. The CA system of the digital TV platform is to realize the control of the broadcast operator's access to the broadcast receiver, and to determine whether the receiver has the authority to receive the relevant TV program. Therefore, CA technology is based on commercial purposes, which not only guarantees the needs of users to freely choose and receive program content, but also protects the interests of broadcast operators, that is, the interests of the licensor and the licensor.
Composition of Digital TV CA (Digital TV Conditional Access) System
A typical digital TV CA (Digital TV Conditional Access) system consists of a scrambled part, an encryption part, and an SMS system. Based on the security of control data transmission, it ensures authorized users to receive, and achieves the purpose of excluding unauthorized users from illegal reception. "Key encryption" system to enhance the security of the system.
Scramble
- The scrambling of the digital TV CA (Digital TV Conditional Access) system is to use the scrambling sequence generated by the pseudo-random sequence to perform bitwise XOR rearrangement on the "0, 1" sequence of the transparent transport stream. Scrambling generally uses a HASH function transform as an algorithm.
- Transmitter: The generation of the pseudo-random sequence is controlled by the initial word, which is composed of a control word and an initial modifier, which can decompose the scrambling sequence into shorter information blocks.
- Receiver: Combine the received control word and the initial modifier into an initial word, and send it to the pseudo-random generator of the decoder to obtain the same pseudo-random sequence as the sender, thereby descrambling to obtain a transparent transport stream.
Encryption
-Service Key SK (Service Key)
The service key is mainly used to encrypt the control word. The service key is generated by the user authorization system, and the service key encrypts the control word to generate entitlement control information ECM (Entitlement Control Message). Therefore, the ECM information contains access criteria information for the service and related information for descrambling.
- Personal Distributed Key PDK (Personal Distributed Key)
In the common network addressing mode, data packets are transmitted according to the user's address, and each network terminal device has a unique and non-repetitive address code, which is used to encrypt the authorization control information ECM. The address of the end user is generally public and encrypted with a sequence associated with this address code. Since this sequence is equivalent to a personal characteristic (unique and non-repeating) determination, it is called a Personal Distribution Key (PDK).
- Subscribers Management System SMS (Subscribers Management System)
-SMS user management system is a database information processing system that implements operation-level management of digital TV services (or "products") ordered by users by integrating network technology and database management technology, that is, a database for user management of pay digital TV services , is to authorize or cancel the authorization with the user or the digital TV service scheduled by the user as the product through the operation of the user account and the CAS (Conditional Access System) interface sends an instruction to the CAS system. The authorization management object of SMS is user or product.
-User Authorization System SAS (Subscribers Authority System)
-SAS user authorization system is an application system applied to the database that stores the relevant information of each smart card (such as serial number, unique identification code, authorization), and authorizes the processed smart card information by extracting the smart card system. The SAS generates the service key according to the instruction of the SMS. The authorization object of SAS is the unique mark or unique serial number of the smart card.
