Decoder Control Word Buffering for Secure Channel Switching
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Solution Overview
Problem
Current conditional access systems for Pay-TV face challenges in rapidly providing and securing decryption keys for multiple channels, leading to delays during channel changes and potential security breaches due to the vulnerability of control words stored in decoders to software attacks and other malicious interventions.
Innovation Solution
A method and decoder architecture that securely manage and store control words by using a key manager to load pairing keys, decrypt, and encrypt control words within a secure register, ensuring each descrambling unit receives the correct encrypted control words chronologically, thereby enhancing security and reducing delays during channel changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If control words are stored in clear form in the decoder for rapid access during channel changes, then channel change speed is improved, but security is worsened due to vulnerability to software attacks
Solution Approach 1:
The system segments control words into multiple encrypted versions, each protected by different cryptographic keys. The decoder stores multiple encrypted control words rather than a single clear form key, allowing rapid retrieval of pre-prepared encrypted versions while maintaining security through cryptographic protection.
Solution Approach 2:
The system performs preliminary decryption and preparation of control words before they are needed for channel changes. Multiple future control words are decrypted in advance and stored in the decoder's buffer, so when a channel change occurs, the pre-prepared control word is already available for immediate use, eliminating waiting time while keeping the system secure through controlled access.
2Productivity
If multiple control words are stored in the decoder for simultaneous channel processing, then productivity is improved, but memory consumption and security risks increase
Solution Approach 1:
The decoder implements a universal control word buffer structure that can serve multiple descrambling units simultaneously. The same buffer memory is shared across different channels and processing units, allowing one memory resource to fulfill multiple functions and support simultaneous channel processing without requiring separate dedicated memory for each channel.
Solution Approach 2:
The system creates multiple copies of control words in the buffer, each copy intended for a specific descrambling unit or time slot. These copies are maintained in encrypted or protected form, allowing the decoder to provide rapid access to appropriate control words for different channels while managing memory usage through efficient copy management and expiration policies.
3Reliability
If control words are changed frequently to prevent hacking, then security is improved, but channel change delays increase due to waiting for next crypto-period
Solution Approach 1:
The decoder performs preliminary decryption of multiple future control words in advance and stores them in a buffer before they are needed. When a channel change is requested, the system checks the buffer for pre-prepared control words that can be immediately applied, eliminating the delay of waiting for the next crypto-period while maintaining the security benefit of frequent key changes.
Solution Approach 2:
The invention introduces an intermediary buffer structure between the security module and the descrambling units. This buffer acts as a mediator that decouples the frequent control word changes from the user-perceptible channel switching. The buffer absorbs the timing differences, allowing rapid channel changes without requiring synchronous updates with the crypto-period, thus eliminating visible delays while preserving security.
Data Source
AI summary
Method for securing control words within a decoder in charge of descrambling digital content protected by these control words, comprising the following steps: for each descrambling unit of this decoder, loading in a directory a pairing key referenced by an identifier associating said key to a descrambling unit; receiving at least one encrypted control word referenced by an indication allowing to identify the descrambling unit for which it is intended; decrypting the control word by using a first key shared with a security module; identifying in the directory the pairing key whose identifier corresponds to the indication of destination associated to the control word; encrypting this control word by using this pairing key; and storing in a register the control word in a chronological and referenced way.