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Conditional Access Systems (CA) in MPEG-2/DVB

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Contents

Conditional Access-CA

Common Interface-CI

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Conditional Access-CA

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Conditional Access System

The primary purpose of a CA system for broadcasting is to determine which individual receivers/ set-top decoders shall be able to deliver particular programme services, or individual programmes, to the viewers.

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Main parts of the CAS in Transmission Side.

1.Scrambler.

2.Encrypter.

3.Subscriber Authorization System (SAS).

4.Subscriber Management System (SMS).

5.Control Word Generator.

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Scrambler

The method of continually changing the form of the broadcast signal so that, without a suitable decoder and electronic key, the signal is unintelligible.

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Encryption.

The method of processing the continuallychanging electronic keys needed to descramble the broadcast signals, so that they can be securely conveyed to the authorized users, either over-the-air or on smart cards.

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Subscriber Authorization System (SAS)

The centre responsible for organizing, sequencing and delivering EMM and ECM data streams under direction from the Subscriber Management System.

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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.

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Main parts of the CAS in Receiving Side.(Settop Box)

Descrambler. Decrypter. Smart Card. Embedded Modem In Settop Box

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Descrambler.

The process of undoing the scrambling to

yield intelligible pictures, sound and data services.

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Decrypter.

The method of decoding the ECM and EMM from the broadcast signal to enable the Video,Audio and Data to the Authorized Subscriber through the Authorized Settop Box and Smart Card.

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Smart Card.

It is used as a token of entitlement to descramble broadcast

signals.. Smart cards can be issued by the Subscriber

Management System which can validate them by

pre-programming them with keys to authorize access to

certain tiers of programmes and/or data services. As part of

the same issuing and validation process, the card may be

personalised to make each one valid for one particular

decoder only

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Typical SMART CARD

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Embedded Modem In Set top Box

Embedded Modem in Settop Box is used to send the Message of Impulse Pay Per View channel selected from the EPG in the STB and send to the Broadcaster SMS system to activate the customer requested IPPV channels to Individual Settop Box.

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CA Mechanisms

Control_Word is used to initialize the Descrambling sequence.

Service-Key is used to scramble the control word for a group of one or more users.

User_Key is used for scrambling the service key.

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Main Components of Scrambling and Descrambling.

Entitlement Management Message(EMM).

Entitlement Control Message(ECM).

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Eentitlement Management Message(EMM).

A message authorizing a viewer to descramble a service. An EMM is a specific component of the electronic key signal and over-the-air addressing information. The EMMs are used to switch individual decoders, or groups of decoders, on or off and are transmitted over-air in encrypted form.

EMM are a function of the service _key and user-key and are transmitted approx every 10 sec.

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Entitlement Control Message(ECM).

A cryptogram of the control word and the access conditions. An ECM is a specific component of the electronic key signal and over-the-air addressing information. The ECMs are used to control the descrambler and are transmitted over-air in encrypted form

ECM are a function of a control_word and the service_key and are transmitted approx every 2 sec.

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Schematic of ECM & EMM generation process.

EncryptionEncryptionControl_wordsECM

EMM

User_key. Service_key.

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Block Diagram of ECM , EMM Generator

IRD/STBIRD/STB

ECMGECMG

EMMGEMMG

Head-end(encoder,

MUX)

SAS

SMSReturn Path

SAS Subscriber Authorization System ECMG ECM GeneratorSMS Subscriber Management System EMMG EMM Generator

Modem

Up-link Down-Link

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ECM & EMM found in the Transport Stream.

PID MVideo 3PID 0 ECM-3EMM-2Audio 3 PID 1 Video 3 EMM-1

Prog 3 Prog 3

CA System-1CA System-1

CA System-2CA System-2

PAT Sections

PMT Sections

CA Sections

Transport Stream

PID

AudioVideoECMPCR

PID M

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ECM, EMM Section.ECM_or_EMM_section() {

Table_id 1 byte 0x80 to 0x8F

section_syntax_indicator 1 bit ‘0’ in ECM & EMM case

DVB_reserved 1 bits ‘1’

ISO_reserved 2 bits ‘11’

CA_section_length 12 bits

CA_data_bytes n bytes (CAS proprietary format)

}

ECM table_id: 0x80 and 0x81 alternatively

used as for “toggle bit”, signalling ECM content change

EMM table_id: 0x82 to 0x8F

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Scrambling and access controlGeneral mechanism

Scrambler

Decrambler

Multiplexer

CWgeneration

ECMgeneration

EMMgeneration

De-multiplexer

Clear Services& data

CWCW

Customer Set Top Box

Service KeyUser Key

Control WordService Key

S.A.S

ECM=f(Control_Word, Service_Key)EMM=f(Service_Key, User_Key)

Scrambled services+ EMMs+ ECMs

Service KeyDescrambler

User Key

EMMs

EMMs User Key

Control WordDescrambler

Service Key

ECMs

Broadcasting Center

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Block Diagram Of Scrambling & Descrambling System.

Modem Modem

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Leading CA Manufacturers

NDS CONAX CRYPTOWORKS NAGARAVISION CANAL+ Viaccess

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Common Interface-CI

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Common Interface CI To decode encrypted Programmes, you need a

subscription to the appropriate broadcaster along with hardware that enables you to use the decryption card (smart card) sent to you by the broadcaster. The first piece of hardware is the Common Interface (CI), which is connected directly to the DVB card. A Conditional Access Module (CAM) is inserted into the CI, and the CAM is used to house the smartcard itself. Unfortunately it is easy to get these names confused. Again and again Conditional Access Modules are referred to as CI modules - which can be confusing, since CIs themselves can also be designed in the form of pluggable modules for example, the Siemens DVB-C module).

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Types of CI

Simulcrypt: A technique allows access to service (program) by multiple CA systems at transmitter. This typically requires a common scrambling algorithm.

Multicrypt: systems. This typically requires that all CA functions (including descrambling) are contained in a detachable module. This is done by means of a standardized interface such as Common Interface in DVB. (DVB-CI, EN50221; Extension,TS 101

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CA Standards

DVB-CSA (Common Scrambling Algorithm)

DVB-SIM (SimulCrypt)

DVB-CI (Common Interface)

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CI Hardware

CI PCMCIA Slot CI Module

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Leading CI Manufacturers

SCM Microsystems NOKIA Iredito Nagaravision CONAX

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Thank You…