Control Message Discrimination for Pay-TV Fast Forward
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Solution Overview
Problem
Current Pay-TV systems using video on demand face issues with decrypting content during fast forward or backward operations due to the limitations of existing filtering methods, which fail to distinguish between identical control messages and result in decryption failures when jumping between cryptoperiods, especially with shorter cryptoperiods.
Innovation Solution
A method for processing control messages that includes a discrimination parameter unique to each message subset, allowing non-consecutive messages to be filtered, enabling decryption key retrieval for secure access to encrypted content, even during fast forward or backward operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If identical control messages are repeated every 50 ms to ensure continuous access, then availability is improved, but the filter blocks duplicate messages causing decryption failures during fast forward/backward
Solution Approach 1:
The control message stream is segmented into distinct subsets, each identified by a unique discrimination parameter. This allows the system to recognize and process non-consecutive messages (skipping odd cryptoperiods during fast forward) while still maintaining the repetition mechanism for reliability. The segmentation enables selective acceptance of messages based on their discrimination parameter rather than blocking all duplicates.
Solution Approach 2:
A discrimination parameter is introduced to distinguish between different subsets of control messages. This parameter changes across message subsets, allowing the filter to differentiate between consecutive messages that should be blocked and non-consecutive messages that should be processed. The parameter change enables the system to maintain message repetition for reliability while allowing fast forward operations to access appropriate decryption keys.
2Reliability
If cryptoperiod duration is shortened to increase security, then security is improved, but decryption during fast forward becomes more difficult
Solution Approach 1:
The discrimination parameter is pre-assigned to each control message subset, creating a predetermined pattern that the filter can recognize. This preliminary assignment allows the system to handle shortened cryptoperiods effectively, as the filter can quickly identify valid messages based on the pre-established discrimination parameter sequence, reducing the complexity of real-time decision-making during fast forward operations.
3Productivity
If the filter blocks identical messages to avoid processing duplicates, then processing efficiency is improved, but fast forward jumps between cryptoperiods are blocked
Solution Approach 1:
The discrimination parameter acts as an intermediary that mediates between the filter's need to block duplicates and the fast forward operation's need to access non-consecutive messages. By comparing discrimination parameters rather than message content alone, the system can efficiently identify true duplicates while allowing legitimate fast forward jumps, thus maintaining both processing efficiency and adaptability.
Data Source
AI summary
A method for processing a set of control messages used to access an encrypted stream by a multimedia unit. These messages include a discrimination parameter having a different value for at least three consecutive non-redundant messages in the stream. The method includes the steps of receiving a current control message; reading the discrimination parameter from the current control message; retrieving from a memory the discrimination parameter from the message processed previously; comparing the current and previous discrimination parameters; and blocking said current control message if the comparison step indicates that the discrimination parameters are identical. The method is characterized in that the discrimination parameter is unique and different for each message in the set of control messages, such that, during the filtering step, the current message and the previously processed message can be non-consecutive in the ordered subset of messages.