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Wednesday, March 6, 2013

What is meant by Conditional Access System?

- Conditional access system or CAS is a system that has been developed as a means for providing the protection to content by setting certain criteria that should be met before the access to it is granted. 
- The concept of conditional access is however related closely to the digital television systems such as the satellite television. 
- The standards for the conditional access system have been defined under the following specification documents of the digital video broadcasting standard (DVB):
  1. DVB – CA (conditional access)
  2. DVB – CSA (common scrambling algorithm)
  3. DVB – CI (common interface)
- All of these standards together define a method for obfuscating a digital television stream, thus providing access to only those possess the ‘valid description smart cards’. 
- All of these specifications are available on the standards page of the DVB web site.
- Conditional access is the result of combination of encryption and scrambling technologies. 
- Firstly, the data stream is subjected to scrambling with a secret key of 48 – bits usually called the control word. 
- The control word is generated in such a pattern in which the successive word cannot be predicted. 
- It is recommended by the DVB that a physical process should be used for that. 
- For a person to unscramble the data stream it is required that he/ she should know about the current control word. 
- In order to provide the protection to control word during the course of transmission, encryption methodology is used. 
- The control word will be de-crypted by the conditional access system only when there is authorization. 
- This authorization is given in the form of EMM or entitlement management message. 
- They are specific for each subscriber. 
- Different ECMs can also transmit the control word at one allowing the usage of many conditional access systems at once and simultaneously. 
- The simulscrypt of the DVB allows all the multiplex operators to cooperate while at the same time saves bandwidth. 
- Channels such as the hot bird satellites and the CNN international make use of several CASs in parallel. 
- The data from the decryption is read from the cards and updated if required through either of the following:
  1. CAM or conditional access module
  2. PC card – format card reader
  3. Built – in ISO/ IEC 7816 card reader
- Conditional access systems include two major types namely analog systems and the digital systems both categorized at shown below:
  1. Analog systems:
Ø  Nagravision
Ø  Videocrypt
Ø  Videocipher
Ø  Eurocrypt
  1. Digital systems:
Ø  Abel Quintic
Ø  ABV (alliance broadcast vision)
Ø  Accessgate

- These systems are the key component for all the digital TV operations.
- Their purpose is to secure the investments of the operators through the encryption of the signals. 
- The payment from the customers in order to watch TV is also ensured by the conditional access systems. 
- But the TV operators usually have limited knowledge about the conditional access systems. 
- Encryption is involved with the whole conditional access system. 
- Operators have the analyzers for finding the cause of the common signal problems. 
- But they do lack tools that can debug the CASs. 
- Most of the conditional access system monitoring tools follow the ETSI TR 101 290 standard (a DVB promoted standard) even though the CAS is not fully covered by this specification. 
- Analyzing tools as such let the operators to know about the problems of conditional access system before the customers notice it. 
- But practically also, it is not possible to take care of all the problems that may affect the subscriber. 

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