Watermarking Encrypted Digital Content in CDNs
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Solution Overview
Problem
Content distribution networks (CDNs) with limited processing capacities cannot efficiently encrypt content or insert unique marks for tracing, as they lack the necessary processing power and security to handle user-specific encryption keys.
Innovation Solution
A method for watermarking encrypted digital content by using a stream cipher process to identify suitable locations for modification within the content, combining watermark values with the encrypted content using a combination function, and enabling retrieval of a unique identifier from the watermarked clear content through reverse operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If content is encrypted with user-specific keys in the CDN, then content tracing capability is improved, but processing capacity requirements and security risks increase
Solution Approach 1:
The patent divides the watermarking process into two independent stages: (1) embedding a position map in the clear content before encryption, and (2) embedding the actual watermark in the encrypted content at the indicated positions. This segmentation allows the CDN to perform only lightweight operations (embedding position maps and simple XOR operations) rather than full user-specific encryption, thus maintaining tracing capability while reducing processing capacity requirements.
Solution Approach 2:
The position map is embedded in the clear content before encryption occurs. This preliminary action prepares the content structure in advance, so that when the content is encrypted and distributed, the watermark can be embedded at the correct positions without requiring complex real-time processing or user-specific key management in the CDN.
2Measurement precision
If user-specific encryption keys are stored in the CDN, then content tracing is enabled, but security risks increase
Solution Approach 1:
The patent extracts the user-specific identification information from the encryption key management system and embeds it directly into the content as a watermark. Instead of storing user-specific keys in the CDN, the system uses a position map combined with simple watermark embedding, thereby enabling content tracing without compromising the security of encryption key management.
Solution Approach 2:
The position map serves as an intermediary structure that enables watermark embedding without requiring user-specific keys in the CDN. The position map contains the necessary information to locate watermark positions after decryption, acting as a mediator between the encryption system and the tracing system without exposing sensitive key material.
3Reliability
If watermarking is performed on encrypted content, then content distribution security is maintained, but processing complexity increases
Solution Approach 1:
Instead of the conventional approach of watermarking clear content then encrypting it (which would require the CDN to handle complex watermarking operations), the patent inverts the process: the position map is embedded in clear content first, then encryption occurs, and finally a simple watermark is embedded in the encrypted content at the pre-determined positions. This inversion simplifies the CDN's processing requirements while maintaining security.
Data Source
AI summary
A method for watermarking an encrypted digital content stored in a content distribution network (CDN) method comprises the steps of receiving in the CDN, a non-watermarked encrypted content and marking metadata, said non-watermarked encrypted content being the result of an encryption of a non-watermarked clear content by a stream cipher process, said marking metadata indicating locations in the content suitable for a modification of said content; using a watermark formed of watermark values and corresponding to a unique identifier; and producing a watermarked encrypted content by combining in the CDN, with a combination function, the values forming the watermark with the non-watermarked encrypted content in locations indicated by the marking metadata.