Nagravision S.a.

Sebastien Robyr

Guy Moreillon

Antoine Burckard

Henri Kudelski

Frederic Thomas

Philippe Desarzens

The invention concerns a method for providing a plurality of receivers with conditional access to broadcast services using a simplified means for managing the control messages required by such conditional access schemes. The method involves providing all information which will allow a registered receiver having the necessary decryption key to access the services without having any prior rights loaded locally. A management center keeps a register of all subscribed receivers, including a list of services to which the receiver is subscribed, and encrypts the services using control words encrypted by the necessary keys. Control messages comprising the control words for decryption are provided within a special channel to which the receiver has permanent access, the special channel being a different one from channels used for broadcasting audio/video services.

Method for accessing services by a user unit

A method of operating by a second processing unit a content recorded by a first processing unit, said first and second processing units having a specific key being managed by a central server. The processing units have access to a removable storage memory intended to record a content ciphered by a content key accompanied by a file associated to the content. The content key is produced by means of a cascaded deciphering starting from the specific key of the first unit of at least two constants provided by the central server and a variable. The content is restored by the second processing unit by means of a cascaded deciphering starting from the specific key of the second unit by using the constants and the variable stored in the file accompanying the content and a transcoding key calculated by the central server.

Method for recording and restoring a ciphered content by a processing unit

A method allows a broadcasted conditional access content accessible at the time of transmission to be also accessible at a later time thanks to intermediate storage on a hard disk of a user unit. The processing method includes the steps of receiving at the user unit a data stream encrypted by at least one control word, at least one control message stream containing the control words, forming an index file, each index comprising an identifier of a control message formed by the extraction of data associated to the control messages and an identifier of the part of the content to which the control message is applied; and, at the time of the deferred processing of the content, extracting at least one part of the control messages and resynchronizing the content with the control messages by the use of the index file, the identifier of the control message allowing the selection of the current control message from a set of control messages at the time of the exploitation of the content identified by the identifier of the part of the content related to this control message.

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Epalinges, Switzerland

Sebastien Robyr