Conditional Access System

• Scope
• Glossary
• Conditional Access Specification
• Requirement to be satisfied
• How it Works?
• Target Users
• How subscriber or customer benefit from using CAS?
• How Broadcasters benefit from using CAS?
• How Cable operators benefit from using CAS?
• How Government benefit from using CAS?

All pay-media operators require a means for ensuring that payment is received in return for the program content they provide. The technical system that achieves this objective is called a Conditional-Access (CA) system.

The definition of Conditional Access is “access is based upon certain condition”. In terms of digital broadcasting, a user gets just what they have ordered for, no more any less. Under a Conditional Access System an authorized receiver can only decrypt the broadcast content.
Conditional-Access (CA) technology offers service providers the ability to grant viewers access to specific programming once payment has been received. Furthermore, CA systems facilitate parental control by restricting access to certain types of programming.

When we decide to implement the Conditional Access, the attention must be paid to the risk and threats involved. The risk is the loss of revenue through signal theft. Conditional Access causes some additional cost to the service provider, which will get reflected to user.

Scope

The Conditional Access technology generally covers the area of Digital Broadcasting like Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB), and Digital Multimedia Broadcasting (DMB) etc . . . . It helps pay-media industry in ensuring the payment received from the viewer in return of program viewed.

Conditional Access technology limits the program viewing to the subscribers, blocking any other access to the program data. The CAS technology is used for digital satellite broadcasting.

Glossary

Control Word (CW): The key used for scrambling and also used at the time of descrambling.
Control Word Generator (CWG): A component which generates the Control Word (every time a unique Control Word) periodically.
Entitlement Control Message (ECM): Private Conditional Access information, which carries the control word in a secure manner and private entitlement information.
Entitlement Management Message (EMM): Private Conditional Access information which, for example, specifies the authorization levels of subscribers or groups of subscribers for services or events.
Subscriber Authorization System (SAS): The centre responsible for organizing, sequencing and delivering EMM and ECM data streams under direction from the Subscriber Management System.
Smart Card (SC): A card which is inbuilt in Set Top Box and each card have a unique ID. This ID is used as a token of entitlement to descramble broadcast signals.
Subscriber Management System (SMS): The business centre which issues the smart cards sends out bills and receives payments from subscribers. An important resource of the Subscriber Management System is a database of information about the subscribers, the serial numbers of the decoders and information about the services to which they have subscribed. In commercial terms, this information is highly sensitive.

Conditional Access Specification

Two main concepts behind this Conditional Access technology:

• Entitlement also known as “Authorization”.
• Scrambling also known as “Encryption of the content”.

Entitlement is a right or privilege. User has to call the service provider to get an entitlement and supplies the information.
Scrambling is the process of transforming information using an algorithm to make it unreadable to anyone except those possessing special knowledge, usually referred to as a scrambling key. The result of the process is Encrypted information.
Scrambling must be done in such a way that the original information can be reproduced without any error or without any loss in quality. Scrambling is usually done on transmission side, using a standard algorithm like AES. To descramble the content at the receiver end some information is needed, that is also transmitted along the scrambling content. The scrambling key is dynamic and changes over a time. These keys, which are used to descramble the data, are never sent directly but are themselves encoded so that an authorized (entitled) receiver only gets the content.
Transmission and Reception are part of same ecosystem. The broadcasters transmits entitlements, the receiver recognizes only its own entitlements. The broadcaster transmits scrambled contents and receiver (if entitled) can descramble the content.

Requirement to be satisfied

Degree of excellence: The scrambling and descrambling processes must maintain the degree of excellence or original quality of the data that is being processed.
Protection of Data: The safety and security must be implemented in such a way that an unauthorized user can not gain access to the service.
Time Delay: The scrambling and descrambling processes must be processed in such a way that the time delay must not occur in broadcasting.
Hardware Requirement: Under the Conditional Access System when scrambled data is broadcasted then there must be some equipment that can decode scrambled data (usually called Set top Box) at the receiver end.

How it Works?

Step 1: Mux collects the raw program data from their respective sources and entitlements (EMMs and ECMs) from SAS and sends it to the scrambler across.
Step 2: CWG generates a control word and sends it to the scrambler. Scrambler will scramble the program data using control word being sent by CWG and send the scrambled data with ECM and EMMs to Modulator across.
Step 3: Modulator modulates the data received and transmits it to antenna.
Step 4: Antenna receives the signals (Scrambled program data) and sends it to Demodulator.
Step 5: Demodulator demodulates the received signals and sends it to Descrambler across.
Figure 2: Implementation of CAS in programme broadcasting.
Step 6: Descrambler first separate the EMMs and ECMs from the scrambled data and then matches the ID that is in EMMs with the ID provided by the smart card. If this ID gets matched then only it descrambles the data using the control word in ECMs.
Step 7: Descrambler then sends this data out to DeMux and DeMux further transmit it to any device like TV, Radio Receiver etc.

Target Users

This paper gives knowledge on conditional access suitable for broadcast networks (e.g. Eureka-147 DAB, XM Radio’s SDARS, etc.). This solution can only be implemented in software industries, although it can utilize external crypto processors and allows a content provider to operate a conditional access system independently of third parties (i.e. DAB). Furthermore, it integrates the consumer into the protection chain, creating a social environment that discourages illegal redistribution of access keys.

How subscriber or customer benefit from using CAS?

Consumers paid for those channels which they want to view only. They don’t bother about all the broadcast channels which are not viewed by consumers (not seen frequently or very rarely seen). Conditional Access causes an additional cost to the service provider which will get reflected to the user that has to be taken into consideration.

How Broadcasters benefit from using CAS?

Broadcasters will address the exact number of sub-scribers with a cable operator. No cable operator would cheat to the broadcasters in terms of subscription fee.

How Cable operators benefit from using CAS?

They pay only a portion of subscription fee to the broadcasters for the absolute number of end users who opt for the channel, rather than all households having cable access.

How Government benefit from using CAS?

These systems also beneficial for government, it generates revenues for a government. The government also facilitates the introduction and development of consumer friendly systems like pay per view.