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The following describes the conditional access process:
*The receiver receives the digital data stream.
*The data flows into the conditional access module, which contains
the content provider's unscrambling algorithms.
*The conditional access module verifies the existence of a smart
card that contains the subscriber's authorization code.
*If the authorization code is accepted, the conditional access module
unscrambles the data and returns the data to the receiver. If the
code is not accepted, the data remains scrambled restricting access.
*The receiver then decodes the data and outputs it for viewing.
A CA system consists of several basic components:
Subscriber Management System (SMS): The SMS is a subsystem
of the CA system that manages the subscriber's information and requests
entitlement management messages (EMM) from the Subscriber Authorization
System (SAS). An EMM provides general information about the subscriber
and the status of the subscription. The EMM is sent with the ECM.
The ECM is a data unit that contains the key for decrypting the
transmitted programs.
Subscriber Authorization System (SAS): The SAS is a subsystem
of the CA system that translates the information about the subscriber
into an EMM at the request of the SMS. The SAS also ensures that
the subscriber's security module receives the authorization needed
to view the programs, and the SAS acts as a backup system in case
of failure.
Security module: The security module, usually in the form
of a smart card, extracts the EMM and ECM necessary for decrypting
the transmitted programs. The security module is either embedded
within the set-top box or in a PC Card that plugs into the set-top
box.
Set-top box: The set-top box houses the security module
that gives authorization for decrypting the transmitted programs.
The set-top box also converts the digital signal to an analogue
signal so an older television can display the programs. .
Smart Cards: For years, smart cards have been used for pay
TV programming. Smart cards are inexpensive, allowing the content
provider to issue updated smart cards periodically to prevent piracy.
Detachable PC cards allow subscribers to use DVB services anywhere
DVB technology is supported.
There are two DVB protocols used by CA systems: SimulCrypt and MultiCrypt.
SimulCrypt uses multiple set-top boxes, each using a different CA
system, to authorize the programs for display. The different ECMs
and EMMs required by each CA system are transmitted simultaneously.
Each set-top box recognizes and uses the appropriate ECM and EMM
needed for authorization. The ATSC standard uses SimulCrypt. MultiCrypt
allows multiple CA systems to be used with one set-top box by using
a PC card with an embedded smart card for each CA system used. Each
card is then plugged into a slot in the set-top box. Each card recognizes
the ECM and EMM needed for authorization.
A typical CA process involves three basic elements: the broadcast
equipment, the set-top box, and the security module. The broadcast
equipment generates the encrypted programs that are transmitted
to the subscriber. When these are transmitted, the set-top box filters
out the signals and passes them to the security module. The security
module then authorizes these programs for decryption. The programs
are then descrypted in real time and sent back to the set-top box
for display
(The above primer has been sourced from the WWW. To know more about
CAS click on this link:
http://searchwebservices.techtarget.com/sDefinition
/0,,sid26_gci331380,00.html
You can also log on to the Conditional Access Forum on the net
at the following URL
http://www.tele.ucl.ac.be/CAS/
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