CI Plus Secure Interface for Audio Video Receiver CAM
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Solution Overview
Problem
The DVB Common Interface (CI) specification has a security weakness that allows decrypted digital content to be intercepted and copied due to the way the host and conditional access module (CAM) interact, which compromises the security of content transfer.
Innovation Solution
The CI Plus specification addresses this by providing a secure interface between the CAM and host, authenticating both devices, encrypting decrypted content, and using a Diffie-Hellman key exchange for secure key management, ensuring that only encrypted data is transferred between the devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the host and CAM interact using the original CI specification with a PCMCIA interface, then interoperability between different CAM and host devices is enabled, but security is compromised as decrypted digital content can be intercepted and copied
Solution Approach 1:
The patent introduces an encrypted communication link as an intermediary between the CAM and host. This intermediary layer encrypts the decrypted content before transmission, preventing direct interception while maintaining the PCMCIA interface for interoperability. The encryption layer acts as a mediator that preserves compatibility while adding security protection.
2Reliability
If integrated devices are used with host and CAM as a single unit, then security over the transfer of unencrypted data is improved, but the advantage of CI interoperability is lost
Solution Approach 1:
The patent segments the security function from the physical integration. Instead of requiring integrated devices, it separates the encryption/decryption functions into the CAM while maintaining the host-CAM modular architecture. The encrypted communication link provides security without requiring physical integration, thus preserving interoperability while achieving security goals.
3Device complexity
If decrypted content is sent in clear form between CAM and host, then device complexity is reduced, but security is compromised
Solution Approach 1:
The patent changes the parameter of data transmission from clear text to encrypted form. By applying encryption to the communication link, the patent transforms the security parameter without fundamentally changing the PCMCIA interface structure. This parameter change adds security while maintaining compatibility with existing hardware interfaces.
Data Source
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AI summary
An audio/video content receiver being configured to receive media content from a content source by a broadcast data path, the media content being arranged as a plurality of media channels comprises a host module having a tuner configured to assign logical channel indices to the media channels to allow selection, at the host module, of one or more of the media channels for reproduction by selecting the corresponding logical channel index, the host module storing channel association data associating the logical channel indices with the received media channels; and a removable conditional access module (CAM), the CAM having an access control unit for decoding access-controlled encoded broadcast content, the host module and the removable CAM being arranged to provide an encrypted communication link for decoded access-controlled encoded broadcast content between the CAM and the host module; in which: the host module is configured to acquire channel association data via the broadcast data path; the CAM is configured to provide further channel association data to the host module; the host module comprises a detector configured to detect a conflict of logical channel index between the channel association data acquired by the host from the broadcast data path and the channel association data provided by the CAM and, in the case of a conflict, to detect one or more unused logical channel indices; and the CAM is configured to select one of the unused logical channel indices for use by a media channel for which the logical channel index defined in the CAM's channel association data conflicts with a logical channel index defined in the host's channel association data.