Patent ID: 7647641

Claim:
Access control method controlling access to a broadcast digital dataflow previously scrambled using an encryption key CW transmitted in encrypted form in an entitlement control message ECM also including at least one access control criterion CA, said numeric data possibly being recorded as such in a receiving terminal or decrypted during transfer, wherein: on transmission: generating an entitlement control message R-ECM c for recording the content of the flow as a function of a recording key KR c and at least one criterion CRR defining a right to record, generating an entitlement control message P-ECM c controlling access to play back the content of the recorded flow as a function of a playback key KP c and at least one criterion CRP defining a right to play back, and on reception: analyzing the message R-ECM c , and authorizing the recording if the criterion CRR is verified, otherwise prohibiting recording, analyzing the message P-ECM c , and authorizing the playback if the criterion CRP is verified, otherwise prohibiting the playback, wherein the keys CW, KR C and KP C are encrypted by a first service key K S , and wherein for a sending phase and for each dataflow: breaking down a scrambling period into a sequence of crypto-periods CP i each defining a validity duration of an individual key CW i , and at each crypto-period change, scrambling the content of the flow using the key CW 1 , and memorizing a value p(i) representative of the parity of i, calculating an entitlement control message SC-ECM i as a function of the previously defined encryption keys CW i−1 , CW i , CW i+1 , the value p(i) and the criterion CA i , said message SC-ECM i being intended to transport access rights to a data segment S i corresponding to at least two crypto-periods, encrypting the keys CW i−1 , CW i , CW i+1 , using the playback key KP c , encrypting the result of the encryption in the previous step using a second service key K′ s , encrypting the result of the encryption in the previous step using the recording key KR c .