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Definition
In recent years, broadcasting and information society services (IS services) have been making ever-increasing use of conditional access devices. This trend is expected to gather pace as the market for these services develops. The conditional access device (CA) provides the user with a technical facility which allows him to determine who has access to electronically-distributed services and under which conditions. In order to improve the legal situation of providers of broadcasting and IS services, the European Commission has recently drafted and adopted a Directive on the legal protection of services based on, or consisting of, conditional access (CAD)This Directive introduces a common standard of legal protection for conditional access devices. However, it focuses exclusively on conditional access devices that serve the remuneration interest of service providers and makes no provision for CA devices that serve other interests.

The traditional role of conditional access is to ensure that viewers see only those programs that they have paid to view. In the digital environment, conditional access has evolved far beyond this role. Today's conditional access systems still support traditional pay TV revenue generation. In addition they enable TV operators to create and protect a unique gateway to the enhanced TV experience - a world of interactive services, including home shopping, games, sports, interactive advertising, and pay-perview programming.
Using today's conditional access systems, you can target programming, advertisements, and promotions to subscribers by geographic area, by market segment, or according to subscribers' personal preferences.You can take advantage of conditional access features to implement flexible program packaging options and support new ways of generating revenue.

Conditional Access System (CAS) is defined as any technical measure and/or arrangement whereby access to the protected service in an intelligible form is made conditional upon prior individual authorization.

The definition of conditional access indicates the two key features of CA - the possibility:
- to exercise control over the access to a service or content which is transmitted electronically
- to control the conditions under which access is granted.

The main conditional access techniques which are currently supported are:
- password devices
- encryption devices.

Evaluating and filtering devices are also increasingly used in the Internet domain, mainly to prevent undesirable material from being delivered to minors, but also for other applications, such as the secure delivery of professional documents. " Push technologies" in the Internet domain could possibly also be assimilated into access control since, on the basis of this technology, content or material is sent only to selected receivers. In the longer term, devices based on biometrics will also be increasingly used to implement conditional access, particularly within the framework of banking services or any other activity, which involves authentication of users, certification of parties and integrity of data.

Fundamentals Of CAS

A conditional access system comprises a combination of scrambling and encryption to prevent unauthorized reception. Encryption is the process of protecting the secret keys that are transmitted with a scrambled signal to enable the descrambler to work. The scrambler key, called the control word must, of course, be sent to the receiver in encrypted form as an entitlement control message (ECM). The CA subsystem in the receiver will decrypt the control word only when authorized to do so; that authority is sent to the receiver in the form of an entitlement management message (EMM). This layered approach is fundamental to all proprietary CA systems in use today.

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