Transparent Encryption for PCM Audio via Bit Truncation
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Solution Overview
Problem
Raw PCM audio data streams are vulnerable to attacks and lack encryption, with existing protocols requiring precise decryption at sample boundaries, which is challenging due to the absence of encryption features in audio interfaces and fixed packet frame sizes.
Innovation Solution
A protocol that reduces the bit depth of PCM audio data to make space for encryption data by truncating bits, using a counter and HMAC signature to authenticate and verify frame boundaries, allowing transparent encryption over existing digital audio links.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If encryption data is added to PCM audio data streams, then security is improved, but the fixed packet frame size and bit depth restrictions cause data loss or require increasing frame sizes which are not permitted
Solution Approach 1:
The patent changes the parameter of bit depth by truncating the least significant bits (LSBs) of audio samples. This allows embedding encryption data within the existing fixed frame structure without increasing frame size, while the truncated LSBs are imperceptible to human hearing. The encryption data is hidden in the vacated bit positions, resolving the contradiction between adding security and maintaining audio data integrity within fixed frame constraints.
Solution Approach 2:
The patent embeds encryption data within the audio data stream itself by nesting the encrypted counter and HMAC authentication code within the truncated bit positions of audio samples. This nested structure allows security data to be hidden within the audio carrier without increasing overall data volume or frame size, enabling secure transmission through existing audio interfaces.
2Adaptability or versatility
If bit depth is reduced to make space for encryption data, then encryption capability is improved, but audio quality may be degraded
Solution Approach 1:
The patent applies local quality by selectively truncating only the least significant bits (LSBs) of audio samples, which are locally imperceptible to human hearing. The more significant bits that determine perceived audio quality are preserved intact. This localized approach allows embedding encryption data in the LSB positions without degrading overall audio quality, as human ears cannot detect the truncation of these low-weight bits.
Solution Approach 2:
The patent treats the least significant bits as disposable elements that can be truncated without meaningful loss. These LSBs are sacrificed to carry encryption data, while the essential audio information in the more significant bits is preserved. The discarded LSBs are effectively replaced at the receiver end with zeros or padding, accepting minimal quality trade-off for gaining encryption capability.
3Reliability
If encryption data is embedded in audio samples, then secure transmission is achieved, but synchronization and frame boundary detection become difficult
Solution Approach 1:
The patent uses a counter that increments with each audio frame to preliminarily mark and track frame boundaries. The counter value is embedded in the encryption data structure, allowing the receiver to synchronize by tracking counter increments. This preliminary counting mechanism establishes frame boundaries before decryption, solving the synchronization problem inherent in embedding encryption data within continuous audio streams.
Solution Approach 2:
The patent implements feedback through HMAC (Hash-based Message Authentication Code) authentication. The receiver decrypts frames, verifies the HMAC authentication code against the decrypted data, and uses this feedback to confirm correct synchronization and frame boundary detection. If authentication fails, the receiver can adjust synchronization, creating a feedback loop that ensures accurate frame boundary detection despite the embedded encryption data.
Data Source
AI summary
Disclosed herein is a data encryption technique that pertains to a data stream that divides into data samples. Each sample is truncated by a predetermined number of bits to make room in the data stream for an encryption data packet. The truncation reduces the resolution of the data in exchange for security features. The encryption data packet includes a counter to prevent replay attacks and an HMAC to verify contents and synchronize the frames of the data stream. The data is encrypted and transmitted to a receiver where the data is played.