BigPatents India

This invention relates to an encryption and decryption method for a conditional access content, in which the content is broadcast in the form of data packets (DP), the previous packets being encrypted by a first key (Kl) associated to a first padding value (PAD1) and to a first encrypted padding element (PADK1) and the following packets being encrypted by a second key (K2) associated to a second padding value (PAD2) and to a second encrypted padding element (PADK2). In this method, the first key (Kl) and the first padding value (PAD1) form a first set of encryption parameters, the second key (K2) and the second padding value forming a second set of encryption parameters. This method includes the steps of (a) extraction of a marker (Mc) from a data packet (DP); (b) creation of a first marking block including the marker (Mc) and the second padding value (PAD2); (c) encryption of the first marking block with the second encryption key (K2); (d) extraction of a second encrypted marking value (MK2) of the first encrypted marking block; (e) creation of a mixed marking block including the second encrypted marking value (MK2) and the first encrypted padding element (PADK1); (f) decryption of the mixed marking block by means of the first encryption key (Kl), in order to obtain a decrypted mixed marking block; (g) extraction of a predetermined part of the decrypted mixed marking block; (h) comparison of this extracted part with a reference value (Mc; PDV2); (i) if the comparison leads to an identity, determination of a new set of encryption parameters different to the first set of encryption parameters and repetition of the steps b) to h) in which the second set of encryption parameters is replaced by the new second set of encryption parameters. No. of Pages : 21 No. of Claims : 16