Patent ID: 8259940

Claim:
Method for broadcasting digital data to a targeted set of reception terminals, in which said data are previously scrambled by a series of control words transmitted in a conditional access entitlement control message (ECM), comprising: on transmission, particularising said entitlement control message by means of a reversible function F whose inverse function F −1 is executable only in terminals of the targeted set of reception terminals using a particularisation parameter specific to said targeted set of terminals, wherein said function F comprises at least one of the following operations: fully or partially encrypt the entitlement control message using particularization methods specific to the targeted set of terminals; and fully or partially pre-encrypt the control words contained in the entitlement control message using particularization methods specific to the target set of terminals; and breaking down the broadcast period into sequence of crypto CPi, generating a control word (CW i ) for each crypto-period CP i fully or partially pre-encrypt said control words, encrypt the pre-encrypted control words, calculating an ECM message as a function of the encrypted control words obtained in the previous step, and as a function of at least one criterion controlling access to the scrambled data, breaking down the ECM message into at least two partial messages, fully or partially encrypting said ECM message, broadcasting the encrypted ECM messages to the terminal on reception, restoring the access control message in its original form only in terminals of the targeted set of reception terminals in which said inverse function F −1 is executable, wherein said function F further comprises at least one of the following operations; reversibly transform the structure of said entitlement control message into a structure that can only be recognised by terminals in the targeted set; reversibly convert the syntax of said entitlement control message into a syntax that can only be recognised by terminals in the targeted set, using the particularisation methods; breakdown said entitlement control message into several parts in a manner specific to the targeted set of terminals using the particularisation methods, and transmit said parts separately from each other.