| 摘要 |
The invention concerns a method for encrypting and decrypting a conditional access content, said content being broadcast as data packets (DP), the preceding packets being encrypted with a first key (K1) associated with a first padding value (PAD1) and with a first encrypted padding element (PADK1) and the following packets being encrypted with a second key (K2) associated with a second padding value (PAD2) and with a second encrypted padding element (PADK2). In said method, the first key (K1) and the first padding value (PAD1) form a first set of encrypting parameters, the second key (K2) and the second padding value forming a second set of encrypting parameters. Said method includes the following steps: (a) extracting from a data packet (DP), a marker (Mc); (b) creating a first marking block comprising the marker (Mc) and the second padding value (PAD2); (c) encrypting the first marking block with the second encryption key (K2); (d) extracting a second encrypted marking value (MK2) of the first encrypted marking block; (e) creating a mixed marking block comprising the second encrypted marking value (MK2) and the first encrypted padding element (PADK1); (f) decrypting the mixed marking block using the first encryption key (K1), so as to obtain a decrypted mixed marking block; (g) extracting a predetermined portion of the decrypted mixed marking block; (h) comparing said extracted portion with a reference value (Mc; PDV2); (i) if the comparison results in identity, determining a new set of encrypting parameters different from the first set of encrypting parameters and repeating steps (b) through (h) the second set of encrypting parameters being substituted by the new second set of encrypting parameters. |
