DIGITAL AUDIO/VIDEO DATA PROCESSING UNIT AND METHOD FOR CONTROLLING ACCESS TO SAID DATA

摘要

The invention relates to a digital audio/video data processing unit and to a method for controlling access to said data. The unit (UT) for processing digital audio/video data encrypted with control words (CW) emanating from control messages (ECM) comprises a unit (DMx) for decrypting the audio/video data (DT), a decompression unit (MPEG), an input/output interface for the processed audio/video data and means for communicating with a security module (SM). The decryption (DMX) and decompression (MPEG) units respectively comprise and encryption unit (EC) and a decryption unit (DC) both of which are provided with at least one personal key (Kec, Kdc) and a common encryption key (Ki). The invention is characterized in that it comprises means for secure transmission of the common key (Ki) and control word (CW) extracted from a control message (ECM) between the security module (SM), wherein the decryption unit (DMX) and encryption unit (EC) use the personal key (Kec) of the encryption unit (EC). Decryption, by the decryption unit (DMX), of audio/video data (DT) with the control word (CW) and re-encryption, by the encryption unit (EC), of said decrypted data with the common key (Ki) are only possible after successful verification of the control word (CW) and the common key (Ki). After temporary storage, the re-encrypted audio/video data (DT) can only be decrypted by the decryption unit (DC) if the common key (Ki) is positively verified by the security module (SM) with the aid of a random number (AL) generated by the decryption unit (DC).