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

2. 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.