Encryption system used to secure content and grant access only to subscribers.

Conditional access or CA provides a method of managing encryption and decryption to allow the operator to control the access to content and services, typically to provide subscription services or to target viewing regions.

Selective access is controlled by a Subscriber Management System or SMS that is used to authorise the user to access services.

The end user or subscriber requires a receiver or set-top box that enables conditional access to such services, often using a smart card and possibly a personal identification number or PIN.

A Common Interface or CI slot provides a standard interface to allow a set-top box to support a variety of conditional access encryption systems.

Examples of conditional access systems include NDS Open VideoGuard, NagraVision Nagra and Canal+ Technologies MediaGuard.