HDCP Receiver Frame Counter Synchronization
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Solution Overview
Problem
In HDCP HDMI systems, transmitter devices that do not adhere to the 200 ms delay after session key exchange may cause link integrity problems due to improper cipher synchronization, leading to decryption issues for receiver devices.
Innovation Solution
A receiver device updates its internal frame counter as soon as it detects an encryption enable control signal, even before completing the session key exchange, ensuring proper cipher synchronization by initializing and incrementing the counter value during the pre-authorization mode, allowing decryption to begin in the post-authorization mode with a non-zero frame counter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the transmitter begins sending encrypted content immediately after session key exchange without waiting 200 ms, then transmission speed is improved, but cipher synchronization reliability deteriorates
Solution Approach 1:
The receiver device performs preliminary actions by initializing and incrementing the frame counter during the pre-authorization mode, before the session key exchange is complete. This allows the receiver to be ready to process encrypted content immediately when the transmitter sends it, eliminating the need to wait for the 200 ms delay while maintaining proper cipher synchronization.
2Measurement precision
If the receiver waits for session key exchange completion before updating internal state, then decryption accuracy is improved, but synchronization speed deteriorates
Solution Approach 1:
The receiver performs preliminary frame counter initialization and incrementing during pre-authorization mode, before the session key exchange completes. This preliminary action ensures that when decryption begins in post-authorization mode, the frame counter is already synchronized with the transmitter, eliminating synchronization delay while maintaining decryption accuracy.
Solution Approach 2:
The invention dynamically adjusts the timing of frame counter updates based on the authorization state. During pre-authorization mode, the receiver updates the frame counter in advance; during post-authorization mode, the receiver uses the pre-initialized counter. This dynamic approach optimizes both synchronization speed and decryption accuracy.
Data Source
AI summary
An HDCP receiver device that receives frames from an HDCP transmitter device. The receiver device has a frame counter that is updated for each frame that is received from the transmitter device and that includes encrypted content, while the receiver device is in a pre-authorization mode. During the pre-authorization mode, the receiver device does not decrypt any received frame bearing encrypted content. While the receiver device waits to transition from the pre-authorization mode to a post-authorization mode in which the receiver device can begin to decrypt any received frames that include encrypted content, the frame counter is updated for each frame received that includes encrypted content. In the post-authorization mode, the frame counter has a nonzero value if frames including encrypted content were received by the receiver device during the pre-authorization mode.