Patent ID: 7882350

Claim:
An encryption and decryption method for conditional access content, in which said conditional access content is broadcast in a form of data packets, previous packets being encrypted by a first key associated to a first padding value and to a first encrypted padding element and following packets being encrypted by a second key associated to a second padding value and to a second encrypted padding element, in which at least said first key and said first padding value form a first set of encryption parameters and in which at least said second key and said second padding value form a second set of encryption parameters, the method comprising: extracting a marker from a data packet; creating a first marking block including on one hand said marker and on the other hand the second padding value; encrypting said first marking block with the second key; cutting said encrypted first marking block in at least two parts, one of said parts having a size of the marker and forming a second encrypted marking value; creating a mixed marking block including on one hand said second encrypted marking value and on the other hand said first encrypted padding element; decrypting said mixed marking block via the first key, in order to obtain a decrypted mixed marking block; extracting a part of the decrypted mixed marking block; comparing the extracted part with a reference value; and if the comparison leads to an identity, determining a new set of encryption parameters different from the first set of encryption parameters and repeating at least one of the extracting of the marker, creating the first marking block, extracting the first marking block, cutting the encrypted first marking block, creating the mixed marking block, decrypting the mixed marking block, extracting the part of the decrypted mixed marking block, and comparing the extracted part in which said second set of encryption parameters is replaced by a new second set of encryption parameters.