Method and processing unit for secure processing of access controlled audio/video data

A method for secure processing of access controlled audio/video data by a processing unit comprising a first conditional access device connected to a second conditional access device provided with a descrambler and a secured processor or secure hardware logic, said processing unit receiving encrypted control messages, the method comprises steps of:

• receiving a control message by the first conditional access device, said control message being structured in an ECM (entitlement control message) format, the control message comprising a first part including first access conditions and, in place of a control word of the ECM format, a second part structured as a control message including second access conditions and a control word, wherein the first access conditions comprise rights for accessing broadcast audio/video data streams, and wherein the second access conditions complete the first access conditions with parameters related to the processing unit;
• decrypting the control message with a key specific to the first conditional access device and verifying authenticity of said control message with first authentication data associated to the control message;
• verifying the first access conditions of the control message in relation to contents of a memory of the first conditional access device and when the verification is successful, transmitting the second part to the second conditional access device;
• receiving the second part by the second conditional access device;
• decrypting the second part with a key specific to the second conditional access device and verifying authenticity of said second part with second authentication data associated to the second part;
• verifying the second access conditions of the second part in relation to contents of a memory of the second conditional access device and when the verification is successful, releasing and loading the control word into the descrambler;
• and
• descrambling the access controlled audio/video data by using the control word and providing said audio/video data in clear to an appropriate output of the processing unit.