As far as the terminal is concerned, the CA used in domestic digital cable TV is mainly divided into two major modes: the first one, the decryption/deauthorization task is completed by the set-top box smart card and the host chip (ie smart card mode); the second, decryption/solution The authorization task is completed by the smart card alone (the card separation method). In theory, the smart card can be directly used in the set top box, so this CA is aptly called a cardless CA.
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Fundamental
Cardless CA is not mysterious. It has been used in satellite digital TV for many years, but it is still a new topic in the cable digital TV market. Taking domestically developed products as an example, the current cardless CA system has the following characteristics:
1. Support dynamic download of encryption algorithms. A part of the algorithm is stored in the terminal, and a part is arranged at the front end for temporary downloading.
2. The shell of the CA is separated from the core. CA provides a unified shell, and the core can be personalized according to the needs of operators.
3. Decryption and descrambling are all done in the set-top box chip.
4. Support the same secret with the card CA.
The workflow of the cardless CA is as follows: First, the front end system sends the EMM (authorization management information) encrypted by the paired private key, and the terminal uses the built-in serial number of the set top box chip to pair with the private key, and stores the encrypted important data in the Flash. Secondly, the CW (control word) of the memory of the front-end system ECM (authorization control system) is encrypted by CK (public key), and the terminal directly transfers the CW to the descrambler.
Analysis of advantages and disadvantages of cardless CA and card CA
The criteria for measuring CA's quality include security, stability, scalability, economics, and technology maturity.
safety. It mainly refers to the difficulty of breaking the CA encryption system. In theory, in a time that is close to infinity, no CA system can be attacked, so the security of CA is actually relative.
First look at the card CA, when the terminal with the card CA is working, because the smart card needs to communicate with the set-top box, there is a risk that the algorithm will be intercepted during the communication process. Although it is theoretically possible to continuously update the encryption algorithm, the receipt of the smart card is equivalent to completely exposing the algorithm to the hacker. In addition, the physical structure of the smart card determines that the capacity of its memory cannot be made very large (generally only a few tens of Kbytes), and it is not too difficult for hackers to find the target code. The hacker who cracked the decryption algorithm can confuse the operator's interests by copying the smart card or sharing the smart card CA information through the network.
The decryption of the cardless CA terminal is performed in the set-top box chip, which not only greatly improves the difficulty of intercepting the encrypted information, but also the hacker needs to obtain the target code to be cracked, and must search in the Flash of several megabytes or even dozens of megabytes. In theory, it is much slower, so the security of cardless CA is much higher than that of card CA.
stability. Since the smart card is connected to the circuit in the set top box through the slot, it is difficult for the card CA to avoid the problem of poor contact. If many users insert the smart card into the slot, the set-top box cannot solve the program because it can't read the EMM information. When the smart card chip is wiped a few times, it can be solved because of the contact problem. In comparison, there is no card CA. As the smart card is omitted, the stability will increase accordingly.
Economical. Since the cardless CA saves the smart card, it can theoretically save the slot and interface circuit corresponding to the smart card. However, in consideration of the same confidentiality as the card CA, I suggest that these slots and interfaces should be reserved. Even so, the cost of a cardless CA set-top box will be reduced by about 50 yuan per card compared to a carded CA set-top box. For this reason, the economy of a cardless CA is not sufficient for the overall translation of the cable in economically underdeveloped areas. The advantages should not be underestimated.
Technology maturity. Considering the maturity of technology, card CA is used in the field of digital TV for a long time, and has a relatively complete DVB standard series support; cardless CA has a short application time in the field of digital TV, especially in the field of cable digital TV, in recent times It only started in the year, and there is no relevant standard in the terminal.
Application. From the application situation, more than 95% of the country's digital rectification areas use card CA; the use of cardless CA only Qingdao Lacey, Guangxi cable network and some satellite and terrestrial digital TV operators.
Cardless CA and soft and hard separation
Since the cardless CA no longer uses the smart card, the principle is a separate application software on the set top box hardware platform, that is, the hardware platform of the CA terminal software and the set top box can be separated soft and hard, and the soft and hard separation can also be Seen as the ultimate form of machine card separation (the function of the size card into the set-top box chip).
The separation of the machine card realizes the separation of the application software such as the set-top box EPG, data broadcasting, VOD and the set-top box, but the CA application software is only separated from the set-top box host and runs on the hardware platform of the set-top box UTI card or CAM card. Therefore, the author believes that the separation of the machine card is an incomplete soft and hard separation. Only the cardless CA can truly achieve the soft and hard separation. The advantage of the soft and hard separation based on the cardless CA is very significant, as follows:
1. Helps to protect the decryption algorithm and key. After the soft and hard separation, the (no card) CA software can be downloaded and executed from the code stream as a separate module. If the hacker intercepts the CA information from the Flash or the code stream, only the encrypted target code can be obtained. Even if the hacker has enough manpower and financial resources, it will take more than half a year to decipher. At the same time, if the decryption algorithm changes every day, the hacker's cracking work has virtually no meaning. It can only be "singular and self-rewarding" the results of his own labor.
Of course, in theory, hackers can copy the cardless set-top box to obtain profits just like cracking a card CA, but each set-top box's CPU, main chip, Flash, etc. have their own ID (identifier), if cloned. They must be done simultaneously by the corresponding manufacturer, which is obviously impossible. Because the above hardware in the set-top box is mostly produced by internationally renowned companies, first of all, these companies will not assist in piracy. Secondly, the cost and time of cloning hardware is much higher than that of cloning originals, and only one clone can be used.
2. Soft and hard separation helps to upgrade the business. Although the soft and hard separation improves the requirements of the application software and hardware platform for the set-top box, it reduces the requirements for the application software. Therefore, once the application software such as CA and EPG is found to be defective, it can be used at any time. In the case of a separate upgrade.
3. Soft and hard separation helps to improve work efficiency. After the soft and hard separation, the hardware and operation platform of the set-top box are provided by the set-top box manufacturer. (No card) CA, EPG, data broadcasting and other application software are developed by a special software company. Since software and hardware manufacturers can concentrate on their own work, Not only will the efficiency be greatly improved, but the cost will also decrease accordingly.
Although there are not many application cases for cardless CA, there are many highlights in the implemented projects, and they are mainly concentrated in the terminal. At present, domestic manufacturers have introduced related chips that support cardless CA, and have achieved complete soft and hard separation, and the chip-based development platform has integrated the basic functions required to design CA. Developing a cardless CA on this platform, the work done is as follows:
1. Using the operating system interface provided by the chip development platform to create various threads and establish an operating environment;
2. Using the driver provided by the chip development platform to complete various actions of receiving the watch;
3. The interface required by the cardless CA manufacturer to provide the chip development platform, such as: start, stop decoding, set age level, working time, obtain authorization information, etc., in order to complete various functions of CA;
4. Compile on the above software and hardware platforms, produce executable files, and the operators separately download them to the set-top box to run.
in conclusion
For a long time, cable digital TV CA technology has been covered with mysterious veil. The author believes that although there is no standard for cardless CA and it is not widely used in China, it has been used by tens of millions of users in foreign countries (such as the wired network in the United States). In China, Shanghai Tiansheng Media (broadcast "European Football"), Hong Kong Yihua Satellite Live Platform in 2005 and the successful application of Qingdao Lacey and Guangxi Cable Network mentioned in the previous article, it should be said that no card CA has a certain The scale of application base. Therefore, the author suggests that operators of cable digital TV operators around the world, especially digital TVs that are just starting or about to start, should give priority to the use of cardless CA solutions, but reserve smart card slots in the set-top box terminals and do a good job with card CA. The same secret; while the ground digital TV that is still in its infancy should try to adopt the cardless CA scheme.
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